Single-strand conformation polymorphism (SSCP) analysis was employed to screen for sequence heterogeneity in the second internal transcribed spacer (ITS-2) of ribosomal (r) DNA of Labiostrongylus longispicularis, a parasitic strongylid nematode occuring in some species of kangaroo in different geographical regions of Australia. The results showed that most of the nematodes screened had different SSCP profiles, which were subsequently shown to correspond to polymorphisms and/or an indel in the ITS-2 sequence. These variable sites related mainly to unpaired regions of the predicted secondary structure of the precursor rRNA molecule. SSCP profiles could be used to distinguish L. longispicularis in Macropus robustus robustus (New South Wales) from L. longispicularis in Macropus robustus erubescens and Macropus rufus (South Australia). This difference corresponded to a transversional change in the ITS-2 sequence at alignment position 82. The study demonstrated clearly the effectiveness of SSCP analysis for future large-scale population genetic studies of L. longispicularis in order to test the hypothesis that L. longispicularis from different geographical regions represents multiple sibling species*.