Molecular genetic studies were carried out on three isolates of Trichinella nelsoni (from Kenya, Tanzania and South Africa) and three isolates of Trichinella T8 (from South Africa and Namibia) from sylvatic carnivores and from a sylvatic swine. A probe (pT7.3) specific for T. nelsoni was obtained by screening a pUC18 genomic library. The pT7.3 sequence was 346 bp in length with an AT content of 70%. The sequence is present approximately 200 times per haploid genome. Southern blot analysis of Hind III digested DNAs of the three isolates of T. nelsoni revealed that the hybridisation patterns of the isolates from Kenya and Tanzania were identical and that they differed from that of the isolate from South Africa, indicating the presence of polymorphism in this species. A pUC18 genomic library of Trichinella T8 was also screened, and one clone (pT8.3) was found to be specific for homologous DNA by dot blot, but Southern blot analysis of DNA samples from eight genotypes showed different hybridisation signals for both Trichinella T8 and Trichinella britovi DNAs. No differences in the nucleotide sequences of the expansion segment V were observed for the T. nelsoni isolates. However, they differed from those of Trichinella T8. The presence of Trichinella T8 in Africa south of the Sahara and its genetic relationship with T. britovi remain unclear and warrant detailed investigations.