Use of 3,4-dichlorobenzenethiol as a trapping agent for alkylating intermediates during in vitro metabolism of nitrosamines. 
Our studies using 3,4-dichlorobenzenethiol as a probe for methylating agent production during exposure of N-nitrosodimethylamine to rat liver S-9 preparations produced results different from those of an investigation reported in the literature.  Methyl-3,4-dichlorophenyl thioether was detected, but the quantities found were not significantly different from the background levels of methylation product detected in the absence of nitrosamine.  Only about 10% of the thioether isolated after incubating N-nitrosodi[14C]methylamine as substrate was radioactive.  The results indicate that the majority of the methyl groups transferred to the sulfur nucleophile in our experiments came from components of the incubation mixture other than the nitrosamine.  Some artifactual methylation was also associated with the analytical procedure.  We conclude that 3,4-dichlorobenzenethiol should be used with caution in studies of alkylation during the in vitro metabolism of carcinogenic nitrosamines.