Abstract: Hamsters or cotton rats-were infected with 3 stocks of L. donovani, one of which had been isolated from an infected Ph. major wui in Xinjiang desert area and 2 from kala azar patients in a mountain area of Gansu and in a plain area of Henan respectively. The purpose of the study was to compare the infectivity of the parasites from different geographic areas through artificial infection of Ph. alexandri. Sandflies were dissected in 4, 6, 8 and 10 days after feeding on the infected animals to observe the growth and development of promastigotes of different isolates in their alimentary tracts. Evaluation was made on 3 aspects, i. e. infection rates, infectiosity and migration of promastigotes in sandflies. It was demonstrated that Xinjiang isolate of L. donovani appeared to be particulary adapted to Ph. alexandri followed by Gansu isolate, the Henan isolate did not show good adaptation to this sandfly, because the number of promastigotes declined and the infection rate dropped after the digestion of the blood meal in the stomach of the sandflies. It seems that the phenomenon was related to the biological characteristics of L. donovani isolates. These results coincided with those of McAb dot ELISA(Qu,1987) and K-DNA dot hybridridization (Lu Hu 1988) for identification of L. donovani from different areas in China, and were also in parallel to the diverse epidemiological characteristics of different kala azar endemic areas (Guan, 1976) .It is reasonable to infer that there may exist different geographical strains of L. donovani in China.