Dimethyl sulfoxide (DMSO) was applied to a 2-cm2 area on the backs of four groups of mice for a 5-min period each day, 5 days per week, for the designated periods: groups I and II--six hairless albino mice (hrhr, c/c) per group--were treated for 8 weeks; group III--three hairless albino mice (hrhr, c/c)--were treated for 4 weeks; group IV--three white mice (ICR Swiss)--were treated for 8 weeks. A group of six untreated hairless albino mice (hrhr, c/c) (group V) functioned as controls for groups I, II and III, and a group of three white mice (ICR Swiss) (group VI) served as controls for group IV. Except for DMSO applications, controls were handled and treated in the same way as the experimental groups. At the end of the experimental periods, the claws of all appendages were removed, measured and average lengths were determined. The claws of group I and group II hairless albino mice were, on average, 2.4-fold longer than the claws of the control hairless albino mice, a significant increase (p less than 0.01) in the average claw length. There was no significant difference in the lengths of the claws of the group III mice after 4 weeks of DMSO application. The claws of group IV (ICR Swiss mice) were, on average, 1.2-fold longer than the claws of the control white mice, representing a significant increase (p less than 0.02) in claw length after 8 weeks of DMSO application.