Inhalation exposure of mice to 50, 200, 500 or 1300 ppm of 1,3-butadiene for 6 h per day for 5 consecutive days caused micronuclei in mouse bone marrow and peripheral blood erythrocytes. The dose response was non-linear. The slope of the curve flattened with increasing exposure concentration. Coat color spots were found in the mouse spot test after exposure of pregnant females on pregnancy days 8-12 to 500 ppm of 1,3-butadiene. Dominant lethal mutations were induced in spermatozoa and late spermatids after exposure of male mice to 1300 ppm with the 5-day exposure regimen. Thus, in the mouse 1,3-butadiene is a somatic and germ cell mutagen.