Mastomys natalensis wcrc infected percutancously with 250 cercariae of Schistosoma mansoni and treated effectively with 5 x 50 mg amoscanatc/kg body-weight 12–16 (1), 28–32 (10,56–60 (111) and 101–105 days p.1. (IV) respectively. Levels of reaginic antibodies (RAb) and homocytotropic IgG antibodies (GAb) were assessed by passive cutaneous anaphylaxis tests (PCA) and compared with those in infected, untreated animals. In untreated animals RAb were first detected in the 6th week p.i. Maximum titres around 1:80 were reached after 100 days. High levels persisted until the end of the experiment 185 days p.i. RAb did not develop after treatment I. After treatmcnt 11 only low PCA titres occurred. After treatment 111 the time course was similar to the controls but levels were reduced. Treatment IV did not interfere with the occurrence of specific RAb.

In the case of GAb, independent of any treatment, after a first peak of PCA titres in the 5th week either a negative pattern or only very low titres were found in week 7. In untreated infected Mastomys GAb levels increased thereafter to maximum titres of about 1:80 at day 70. Later than 100 days p.i. relatively constant titres were observed. The second rise of antibody levels did not occur after early treatment. After treatment 11 only low transient titres developed. Animals treated in the early patcncy (III) showed reduced PCA titres and were negative at the end of the observation period. Treatment given 101 to 105 days pi. rather enhanced the development of GAb.