Chlorine and bromine can react with natural organic substances in source waters to form haloacetic acids, major disinfection by-products of water chlorination. Several toxic effects including testicular damage have been attributed to the chloroacetic acids but little information is available on the bromine analogues. In this report we present the results of acute toxicity and acute spermatotoxicity studies of monobromoacetic acid (MBAA) and dibromoacetic acid (DBAA). In adult male rats the acute oral toxicity of MBAA was 10-fold that of DBAA (LD50 177 vs 1737 mg/kg). No reproductive-related endpoints were affected in rats given a single dose of 100 mg MBAA/kg or 14 daily doses of 25 mg MBAA/kg/day. In rats dosed with DBAA, serum testosterone fell to 17% of control 2 days after a single dose of 1250 mg/kg but returned to control levels by Day 14. Marked effects on sperm motion were seen on post-treatment Days 14 and 28. Degenerative flagellar changes in cauda sperm were present on Day 14 while abnormal sperm head shapes and flagellar degeneration were observed in both caput and cauda sperm on Day 28. Histopathology indicated altered spermiation at all time-points as evidenced by retention of Step 19 spermatids beyond Stage VIII of the cycle of the seminiferous epithelium. Disorganization, distortion, and degeneration of late spermatids were also observed. On Day 14 structures resembling residual bodies were rarely seen in the testis but were numerous in the epididymis. Caput sperm counts were decreased on Day 2 and cauda sperm counts were decreased on Days 14 and 28.(ABSTRACT TRUNCATED AT 250 WORDS)