Phenotypes of species hybrids created from in vitro fusion of zoospores from Phytophthora nicotianae and P. capsici were characterized and compared. The species hybrids were created as part of a study of sources of genetic variation in populations of the parent species that are pathogenic over a similar range of plants. Four isolates of species hybrids proved to be similar to both P. capsici and P. nicotianae in relation to vegetative and reproductive morphologies. As in a previous study, DNA of P. capsici was detected more readily than that of P. nicotianae in all hybrid isolates. In the present study, DNA of P. nicotianae was detected in three of four hybrids by hybridization of RAPD-PCR products with species-specific DNA from P. nicotianae. By thermal denaturation analyses, DNA melting temperatures and GC contents of parent species and species hybrids were similar. The mean GC content of 47·2% was similar to GC contents reported for other Phytophthora spp. Additionally, the distributions of GC-rich regions of hybrids were more similar to the distribution in P. capsici than in P. nicotianae. By these molecular analyses, the hybrids were shown to be more similar to P. capsici than to P. nicotianae. Even though interspecific somatic fusion is likely to occur rarely under natural conditions, it could contribute to the genetic diversity of heterothallic species of Phytophthora.