When skin fibroblasts from patients with Duchenne muscular dystrophy were treated with trypsin in the presence of divalent cations, they detached more rapidly from the substratum than did fibroblasts from normal individuals of similar age, sex, and passage number. This difference was observed when either the time of incubation or trypsin concentration was varied. The ease of detachment of both normal and dystrophic fibroblasts varied somewhat with culture age and plating density, although detachment was always greater for fibroblasts from dystrophic individuals. If the trypsin treatment was carried out in the absence of divalent cations, both types of fibroblasts detached rapidly from the substratum, suggesting that a divalent-cation dependent cell-substratum adhesion mechanism is altered in Duchenne muscular dystrophy fibroblasts.