OBJECTIVE Atopic eczema/dermatitis syndrome (AEDS) is often the first manifestation of atopic disease in children. Food hypersensitivity should be considered in approximately 40% of these patients. AEDS children with cow's milk allergy are commonly prescribed a hydrolyzed formulas or amino acid-based formulas for an alternative protein source. The aim of this study was to investigate hypersensitivity to extensive hydrolyzed casein and whey proteins in AEDS children with cow's milk protein allergy (CMA). METHODS The study included 67 hospitalized children with AEDS (m/f--43/24), aged 1-28 months (mean 11.34 +/- 8.52) and CMA confirmed by oral food challenge. All patients were treated with extensively hydrolyzed formulas: 48/67 children with casein hydrolysates and 19/67 children with whey hydrolysates. RESULTS In most of studied children we recognized severe AEDS (SCORAD Index: mean 55.41 +/- 17.4; 95% CI 51.17-59.66) with elevated total IgE (mean 432.98 +/- 1030.46; 95% CI 181.63-684.33). In 22/67 children (32.8%) we established diagnosis of hypersensitivities to hydrolyzed formula (HHF): in 17/22 to casein hydrolysates, in 4/22 to whey hydrolysates and in 1/22 to amino-acid based formula. Children with HHF did not differ in the severity of AEDS evaluated by SCORAD (57.18 +/- 16.59 vs 54.56 +/- 17.90), the serum level of total IgE (603.9 +/- 1253 vs 349.4 +/- 906.1) and the time of breast-feeding (4.4 +/- 4.0 months vs 6.8 +/- 7.28). They differ in the number of plasma eosinophils and positive correlation between number of eosinophils and serum level of total IgE (p<0.05, r=0.46 vs r=0.07). CONCLUSIONS Children with moderate or severe atopic eczema/dermatitis syndrome can demonstrate hypersensitivity to hydrolyzed formula recommended for therapeutic indications.