Ribotyping performed with six restriction endonucleases was used to study the molecular epidemiology of shigellosis in Asturias, Spain. The series included Shigella sonnei from 34 sporadic cases, 3 outbreaks and 3 reference strains, and S. flexneri from 13 sporadic cases and 1 reference strain. The S. sonnei strains were grouped into 5 ribotypes with Sal I, 4 with Hind III and Pvu II, 3 with Bgl II and EcoR I and 2 with Hinc II (Discriminatory Index (DI) between 0·54 and 0·14); the S. flexneri into 5 ribotypes with Sal I, Hinc II and Hind III, and 4 with the other enzymes (DI = 0·71–0·63). The combination of results for 2 or more enzymes facilitated an additional discrimination, the highest values in S. sonnei were for the 6 enzymes (16 types, DI = 0·91) and in S. flexneri for some combinations of 3 or more enzymes (7 types, DI = 0·81). Ribotypes with the 6 enzymes defined 16 clonal lines in S. sonnei and 7 in S. flexneri, which showed a different degree of genetic heterogeneity, and all the lines of each species falling into a different cluster. No line appeared as clearly endemic in the bowels of Asturian people.