DNA adduction in urothelial cells of a person exposed to 4,4'- methylene-bis(2-chloroaniline) (101144) (MOCA) was studied. Urine samples were collected from a 30 year old male worker 4, 18, 24, 44, 49, 73, 98, 138, 145, 215, 354, 399, 407, and 408 hours after he was accidentally exposed to molten MOCA. Urothelial cells were collected by filtering the samples through 5 micrometer pore size cellulose nitrate filters. The DNA was extended and analyzed for DNA/MOCA adducts by phosphorus-32 post labeling and thin layer chromatography. A single adduct that cochromatographed with N- (deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl-alcohol was detected in urine samples collected 4 to 98 hours after exposure. The maximum adduct concentration was 516 adducts/10(8) nucleotides occurred 4 hours post exposure. At the 18 hour sampling point, the adduct concentration had decreased five fold compared to the concentration at 4 hours. At 98 hours the adduct concentration was 6 adduct/10(8)nucleotide. The authors conclude that the results suggest that MOCA may be genotoxic and supports the hypothesis that MOCA is a potential bladder carcinogen.