The inheritance and occurrence of various subtypes of epidermolysis bullosa (EB), the clinical and ultrastructural features of the disease (I) and its connections with possible defects in collagen metabolism were studied in the population of Finland. Information was obtained on 40 families with 121 diseased members alive. Genealogical analysis of these revealed 55 additional cases of probable EB. The series probably includes all the subjects affected by the recessively inherited types living in Finland in 1971-1980. Subjects with dominant types often have such a mild disease that they cannot all be included in a retrospective study. Eleven of the subtypes of epidermolysis bullosa were represented, and two families were found not to belong to any previous subgroup and were regarded as so far unclassified. The largest morphological group among the intraepidermal types, with seventeen families altogether, represented the pattern of cytolysis, acantholysis and dyskeratosis corresponding to EB simplex Köbner and Weber-Cockayne. In six families tonofilament clumping was the main morphological finding and the clinical picture in these cases was EB herpetiformis Dowling-Meara (I, II). Tonofilament deficiency, found in one family with congenital skin defects, was classified as EB Bart, and in one family a deficiency in one enzyme of collagen synthesis, galactosylhydroxylysine glucosyltransferase activity in skin and serum, was found to correlate significantly with severity of EB simplex Köbner (VI). In three other EB simplex families no such deficiency could be shown, suggesting that it may be of aetiological significance in some but not all EB simplex cases. In the junctional group three families with six dead infants were classified as EB atrophicans gravis-Herlitz and one live member with a hemidesmosome defect as EB atrophicans mitis. There were also two unclassified cases with junctional splitting and normal hemidesmosomes. This suggests greater heterogeneity in this group than has hitherto been thought. Among the dermal forms of EB there were eight families with dominant EB dystrophica Cockayne-Touraine and Pasini with 55 patients altogether. In one family both of these clinical expressions were found, suggesting a common gene source. Two families represented recessive EB dystrophica and one also contained a patient with acquired EB (III). In this last case the disease broke out in connection with parturition. Active collagenase and compensatory collagen production were increased in the cases of recessive EB dystrophica and in that of recessive EB atrophicans mitis (V).(ABSTRACT TRUNCATED AT 400 WORDS)