Abstract: Fourteen compounds related to rosaniline were tested for their chemotherapeutic effect on mice against Schistosoma japonicum.It has been found that the therapeutic effect of purified para- rosaniline approaches that of rosaniline;purified rosaniline from which pararosaniline had been removed is less effective;and the rest are ineffective. Some relationships between the Chemical constitution and the antibilharzial activity of rosani- line may be deduced as follows:Alkylation or arylation of the amino groups causes loss of the therapeutic effect.Removal of the methyl group from the benzene ring leads to increase in thera- peutic effect.Introduction of acidic radicals into the benzene rings results in loss of activity. The quinoid structure does not appear to be an essential structure,but amino groups are pro- bably necessary.It may be considered that the antibilharzial activity of rosaniline is not due to the common characteristics of basic dyes,but is based on the specificity of its chemical constitu- tion. Combined medication of rosaniline with tartar emetic has resulted in synergism of its thera- peutic effect against experimental schistosomiasis in both rabbits and dogs.