Gelatin was chemically modified by crosslinking samples with one of a number of bifunctional reagents as was done earlier in a processing technique used to improve mechanical properties through chain orientation. The effects of this crosslinking on the biodegradability of the resulting films were evaluated in the laboratory by exposing them to lake and river waters for 10 days with or without inoculation with periphyton organisms. Biodegradabilities were assessed by weight losses of the films and by measurements of dehydrogenase activity of biomasses taken from their surfaces. The extent of biodegradation depended on the type of crosslinking agent and the presence or absence of the periphyton. The gelatin films crosslinked with formaldehyde, glyoxal, or glutaraldehyde were the slowest to biodegrade; complete degradation required 8-10 days. In contrast, the most biodegradable was the gelatin crosslinked with hexamethylene diisocyanate, which required only 3-4 days. The uncrosslinked gelatin and the gelatin crosslinked with butadiene diepoxide and diepoxyoctane were intermediate, degrading in 5-7 days. The dehydrogenase activity paralleled the weight losses but rapidly decreased when the amount of gelatin remaining was small. (C) 2000 John Wiley & Sons.