The acute toxicity of two degradable polymers, a 70:30 poly (L-D, L-lactide) (PLDLA) and a 90:10 poly(L-lactide-co-glycolide) (PLGA), was evaluated by the agar diffusion test and the filter test with L929 mouse fibroblasts. Extracts of the materials prepared in phosphate-buffered saline at 37 and 70 degrees C were assessed for mitochondrial succinate dehydrogenase activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT assay) and the incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA of BALB 3T3 cells. Both materials revealed no signs of cytotoxicity during the agar diffusions and filter tests. In the MTT and BrdU assays PLDLA and PLGA showed similar results. Cells treated with extracts prepared at 37 degrees C caused slight stimulation of mitochondrial activity. In contrast, cells incubated with the 70 degrees C media revealed a concentration-dependent decrease of mitochondrial activity. DNA synthesis was significantly decreased by the 37 degrees C extracts. As in the MTT assay, the effect of the extracts prepared at 70 degrees C was significantly greater. From these in vitro results it is suggested that PLDLA and PLGA have satisfactory biocompatibility. High concentrations of the degradation products, however, had a toxic influence on the cell culture systems used.