Genetic diversity in strains of human group A rotaviruses was analysed by phylogenetic methods. The study material comprised 109 serotype G1 or G4 rotavirus samples isolated in Finland during 1986-1990. Parts of the coding regions of rotaviral genome segments 4 and 9, which encode proteins with serotype specificity, the spike protein VP4 (P serotype) and the outer capsid protein VP7 (G serotype), respectively, were sequenced. As determined by analysis of segment 4 sequences all G1 strains and all except one G4 strain showed P[8] specificity, the one being of P[6] specificity. The G1P[8] strains could be further differentiated into four groups based on segment 9 sequences, while G4P[8] strains formed only one group. Type P[8] (G1P[8] and G4P[8]) strains formed two main groups based on segment 4 sequences, suggesting free segregation of segment 4 between these G strains. Most global G1, G4 and P[8] strains in GenBank/EMBL originating from the 1970s to the present co-clustered with these groups, suggesting that the groups exist as relatively stable lineages. No linear accumulation of nucleotide substitutions was detected in strains of one serotype during the study period. Also, the deduced amino acids of the antigenic regions A, B and C of VP7 were nearly conserved within the phylogenetic lineages. Interestingly, only short amino acid sequences were necessary to divide the e-types correctly into phylogenetic lineages. These amino acid signature motifs were located in aa 29-68 of VP7 and aa 121-135 of VP4 of the G1 and P[8] lineages, respectively.