The Balb/c strain mice were immunized by single intraperitoneal administration of 0.2 cm3 of 10% sheep erythrocyte suspension (SRBC). Tołpa Peat Preparation (TPP) used in the study was a peat-derived substance obtained in prof. St. Tołpa's laboratory. It was given to mice intraperitoneally, 4 times at 24-hour intervals. The first dose was administered 2 hours before immunization. Testing was performed with the following doses: 0.5, 2.5, 5, 10, 25, 50, 100 and 250 mg/kg. The determinations comprised the number of spleen cells producing anti-SRBC haemolysins, the level of serum haemagglutinins to SRBC (19S+7S and 7S types) and the percentage of splenocytes forming spontaneous E-rosettes. It was found that the effect of TPP on these immunologic parameters of the mice immunized with SRBC was dose-dependent. The effect potentiating the humoral response occurred for the doses of 0.5-10 mg/kg. The doses of 25 and 50 mg/kg did not affect the immunologic response to SRBC, while the doses of 100 and 250 mg/kg had a suppressive effect. The impact of TPP on the percentage of splenocytes forming E-rosettes was also dose-dependent, but in this case stimulating activity was observed for the doses of 2.5-25 mg/kg.