The hypnozoites of different isolates of P. vivax from Shenzhen and Shixin, Guangdong Province, Changsha, Hunan Province and Yincheng, Hubei Province of China in cultured materials were observed employing immunoperoxidase staining method. The percentages of hypnozoites among exoerythrocytic stages were 40.1, 43. 5, 50. 6 and 57. 1 %, respectively,indicating that the percentage of hypnozoites and the latitude are in positive correlation. The equation is y= - 6. 68+ 2. 05x. When the dlfference in latitude of Plasmodium vivax isolate source was more than 5?, a significant difference in the percentage of hypnozoites in various geographic isolates was found. However, the average diameters of hypnozoites and schizonts among various geographic isolates showed no significant difference. The results showed that ln the regions north to the Yangtze Rlver, the proportion of hypnozoite in the liver stage of P.vivax was larger than those in the southern China, being consistent with the clinical manifestations.