Chlorambucil induced a number of recessive visible mutations in the mouse. Induction of these mutations was studied in two mating schemes, each designed to recover mutations after two intercrosses. In scheme 1, 10 mutations were detected in 82 mice; in scheme 2, 1 mutation was detected in 19 mice. We have estimated that the proportion of gametes carrying a recessive visible mutation may be as high as 25% after a dose of 10 mg of chlorambucil per kg to early spermatids. Seven of these mutations caused morphologically distinct abnormalities, including (i) a cerebellar abnormality similar to that expressed in homozygotes for the reeler (rl) mutation; (ii) open eyelids at birth; (iii) a rostral head hemangioma; (iv) abnormally small spleens, anemia, and umbilical hemorrhages; (v) immobility at birth; (vi) polycystic kidneys; and (vii) a circling behavior. Four additional mutations resulted in growth retardation and a runting syndrome. Because, in earlier studies, all molecularly characterized mutations induced by chlorambucil in poststem cells have proved to be deletions, these recessive visible mutations are probably deletions as well. These mutations may be useful in isolating and characterizing the genes responsible for the observed phenotypes.