Biomphalaria alexandrina are known to be intermediate hosts for both Schistosoma mansoni and Echinostoma liei. RAPD-PCR assay offers a new approach to host-parasite relationships. This was performed by investigating the genetic variation and compatibility among S. mansoni, E. liei and their intermediate host B. alexandrina with special emphasis on variations occurring in snails infected with S. mansoni and/or E. liei. Six primers were screened for DNA analysis and gave total patterns from 28 to 37 reproducible bands for each species. All specimens analyzed by the RAPD-PCR gave interpretable electrophoretic banding patterns that were polymorphic and compatible in the amplified products of these primers within each species.