Abstract:Fifty-eight isolates representing three Cronartium species, the pine-stem rust fungi, collected from diverse pine hosts and geographic origins in China were evaluated for their interspecific and intraspecific variation by isozyme analysis. Eight of the 1 3 examined enzymes produced visible banding patterns. Among them the esterase (EST) patterns provided the best differentiation , distinctly seperating C. ribicola, C .flaccidum and C.quercuum from one another. No isozymic variants were detected in the 1 6 C. ribicola isolates from different locations in northeastern China, demonstrating that the genetic variation in the population of this rust fungus in this area is small. Although some variants were found in the 1 7 C.quercuum isolates from mongolian pine in northeastern China, the isozyme patterns of the majority of the isolates, however, were uniform with those of the isolates from Masson‘s pine in eastern and central China, indicating the validity of considering .C.flaccidum occurring in China as a complex species. Nineteen C.quercuum isolates collected from diverse hosts and loca-tions in northeastern , eastern and central China, except some of those from mongolian pine, also provided uniform isozyme patterns and did not show the isozymic variability as big as that previously reported in northern American C. quercuum Population, possibly implicating the occurrence of C.quercuum in China is a more recent event than that in northern America .