BACKGROUND Skin prick-test has been accepted as one of diagnostic criteria for atopic diseases. In accordance with the recommendations of the EAACI (European Academy of Allergy and Clinical Immunology), the Subcommittee for skin testing, allergen specific skin prick-test should be estimated in relation to positive control (histamine hydrochloride in the HEP system/histamine equivalent prick/) [1-4]. The purpose of this study was to establish a recording system of skin sensitivity to allergen by using HEP method in our patients. METHODS The study was performed in 75 persons (49 females, 26 males, mean age 34.6 years) suffering from atopic diseases (hay fever, allergic asthma or rhinoconjunctivitis) and susceptible to one of pollen allergens. Skin prick tests were performed and recorded as said before [2-6]. We used a house standardized (Torlak Institute) allergen solution of 5000 AU/mL (pollen of Dactylis glomerata, Lolium perennae, Phleum pratense), 7500 AU/mL (Phleum pratense) and 10,000 AU/mL (Phleum pratense) and histamine-hydrochloride solution (1 mg/mL and 10 mg/mL). Total and allergen specific serum IgE was made before the study by ELISA immunoassay (Pharmacia, Uppsala, EIA RAST Phadesim) in all selected persons and results were recorded in Phadebas RAST unit given by the manufacturer. According to the serum concentration of specific IgE, patients were classified into groups (low susceptibility, intermediate sensitivity and highly susceptible persons). Skin reactions were recorded according to histamine skin sensitivity (as reaction equal or larger in diameter than histamine papule). Additionally, measured allergenic and histamine wheal were sorted and frequency of positive tests was calculated. Skin testing was performed with the approval of the Ethic Committee of our Centre and with the written patients' consent. For statistical analysis we used chi 2 test, regression analysis and Kolmogar-Smirnov nonparametric test. Results for the confidence of 95% (p < 0.05), were considered significant. RESULTS In a group of 30 persons, susceptible to Phleum pratense pollen (Table 1, Graph 1 and 2), it was found that the number of positive tests was equally distributed among groups; it was dependent on the allergen concentrations, and was higher when using H1 (p < 0.01). When H10 was used as reference solution, only allergens of the highest concentration provided a significant number of positive tests (p < 0.01). There was no difference among groups of patients depending on the concentration of used histamine solution. In all 75 persons, we estimated skin-prick test performed by allergen solution of 5000 AU/mL and compared it with HI reaction. It was calculated that the most frequent histamine papule diameter was 3 mm and this value was farther used as the end-diameter in HEP system. Patients were classified in groups on the basis of serum IgE concentrations (RAST). The estimation of criterion positivity revealed the highest significance by using criterion Ap > Hp (p < 0.001). At the same time, if the criterion Ap > 2Hp was used we were sure that 99% of our patients were highly sensitive to allergen we tested. CONCLUSIONS In the study it was established that allergen concentration of 5000 AU/mL and histamine solution of 1 mg/mL are sufficient to estimate skin-prick test in the HEP system. We found that the end diameter of histamine-papula was 3 mm. This finding suggests the good utility of HEP system. In addition, it has been proven that absolute value of papula diameter is not a critical parameter for the estimation of positivity or discrimation among patients regarding their susceptibility to allergen. By this system we found that criterion Ap > Hp, provides a significantly higher number of positive tests (p < 0.001). The recommended criterion Ap > Hp gives no discrimination among tested groups of patients, while using the criterion Ap > 2Hp we diagnosed highly susceptible persons (p < 0.01). (ABSTRACT TRUNCATED