Abstract: It has been reported by the authors that monoclonal antibody L12G9 produced from target antigens of L. donovani promastigotes, was very useful for detecting promastigotes from artificially infected sandflies. In the present study, detection of promastigotes from artificially infected sandflies by McAb showed that the positive rate correlated with the infection duration of sandflies. 4 days after feeding on infected Chinese hamsters, the sandflies were lightly infected with L. donovani promastigotes with a positive rate of 15.9%, but 10 days later, the sandflies were heavily infected, the positive rate being 100%:Observation has been made on the relationship between the number of promastigotes and mouse blood dilution. The results showed that satisfactory results could be obtained by using monoclonal antibodies in the detection of L. donovani, the number of promas tigotes should be over 1 × 107/ml, and the blood meals in sandflies completely digested.If very few promastigotes were present in naturally infected sandflies before identification by monoclonal antibody, the parasites must be grown in NNN medium. Positive result could then be obtained.