The methylations of trematode genomic DNA were analyzed using restriction enzymes and Southern blot hybridization. Restriction enzymes MspI, HpaII, HhaI were used to probe CpG methylation while MboI, Sau3A, DpnI were used for A methylation. The results revealed that Opisthorchis viverrini, Fasciola gigantica and Gigantocotyle siamensis had neither CpG nor A methylations. The presence of highly repeated DNA elements was also demonstrated in O. viverrini genomic DNA.

Riboprinting is one of several molecular methods that can generate comparative data independently of the complexity of the organism's morphology. Restriction fragment length polymorphism (RFLP) profiles derived from digestion of polymerase chain reaction (PCR) products of the ribosomal 18S from Leishmania spp. yields a typical ‘riboprint’ profile that can vary intraspecifically. A selection of 76 stocks of L. major and L. tropica, isolated from patients with cutaneous leishmaniasis, was analysed by riboprinting to assess divergence within and between species. L. major and L. tropica could be easily differentiated from each other. Analysis of PCR–RFLP profiles indicated that stocks of Leishmania spp. could be broadly partitioned into 2 species corresponding to L. major and L. tropica. To test if ribosomal 18S sequences were homogeneous within each species, several isolates of each of the Leishmania spp. were digested. Interpretation of the riboprint profiles of the 18S independently amplified by PCR, there would appear to be one restriction pattern present within each Leishmania spp. Homogeneity within copies of the ribosomal 18S within a single genome has, therefore, been demonstrated. The species designation established by riboprinting results were in agreement with the zymodeme analysis of the same isolates. The restriction patterns produced were simple, reproducible and easy to interpret.

Restriction fragment length polymorphism (RFLP) was studied for six populations of the polytypic snail Neotricula aperta using seven different restriction enzymes. Samples of all three strains of N. aperta from north-eastern Thailand were examined, as well as topotypes from southern Laos and material from Kampuchea and central Laos. Genetic distances were estimated as Nei & Miller's (1990) distance ×100 (D). The samples were taken from the Mekong, Mul and Xé-Bang-Fai (XBF) rivers of the lower Mekong basin. The γ-strain of Kampuchea and southern Laos has been shown to act as intermediate host for Schistosoma mekongi. The least amount of genetic divergence was found where the α-strain was compared with other taxa (D, 2.1–3.7), and the largest values for comparisons involving samples of the XBF strain (D, 2.1–6.4). Large distances were apparent between the b-strain and all the γ-strain populations (D, 4.0–5.5). The β- and XBF-strain may represent a pair of sibling species with respect to N. aperta. The γ-strain population of north-eastern Thailand comprised two cryptic taxa which were relatively well diverged (D = 1.6). Only one of these cryptic taxa showed close affinity with other γ-strain taxa; this finding may be important in the control of Mekong schistosomiasis.