Phenmedipham [methyl-3-(3-methylphenylcarbamoyloxy)carbamate] is used as a herbicide, especially in the growing of sugar beet and strawberries. During metabolism of the substance in rats, the two carbamate moieties of phenmedipham are cleaved and the metabolites methyl-N-(3-hydroxyphenyl)-carbamate, m-aminophenol and hydroxyacetanilide are formed. These compounds and their conjugates are excreted in urine. Additionally, it has been suggested that m-toluidine is formed during metabolism. For the first time it has been possible to detect this metabolite in the urine of workers after agricultural use of phenmedipham. The concentrations of m-toluidine in urine were significantly higher in persons occupationally exposed than in controls. The median values for each group were 0.36 microg/l and 0.16 microg/l, respectively. This means that persons not exposed to phenmedipham also excrete m-toluidine, possibly as a result of the uptake of pesticides like phenmedipham from the diet.