The results of biological monitoring by assay of urinary 3,5,6‐trichloro‐2‐pyridinol and alkyl‐phosphates (DMP, DMTP) in groups of 9 and 2 workers exposed to chlorpyrifos‐methyl during vine spraying and manual leaf thinning 5–11 d after spraying, respectively, are reported. The results are compared with those of a control group of 46 subjects not occupationally exposed to organophosphate insecticides. Significantly higher urinary excretion of metabolites (Mann‐Whitney V‐test) was found in both groups than in controls. Levels of 3,5,6‐trichloro‐2‐pyridinol (mean ± SD) were 15.9 + 10.6 nmol/g creatinine (n= 33) for controls, 92.4 + 162.5 nmol/g creatinine (n= 20) for manual workers, and 675.5 + 1110.8 nmol/g creatinine (n= 48) for workers spraying and mixing the insecticide. Levels of DMP (mean ± SD) were 63.8 + 100.1 nmol/g creatinine (n= 42), 123.0 + 79.0 nmol/g creatinine (n= 20), and 577.2 + 1003.2 nmol/g creatinine (n= 61), respectively, for the same 3 groups. Levels of DMTP (mean ± SD) were 153.4 + 164.4 nmol/g creatinine (n= 43), 489.3 + 288.3 nmol/g creatinine (n= 20), and 297.6 + 2 75.4 nmol/g creatinine (n= 61), respectively, for the same 3 groups. Good correlations were found between urinary excretion of 3,5,6‐trichloro‐2‐pyridinol and DMP (r= .776 for manual workers; r = .775 for workers mixing and spraying the insecticide) or DMTP (r= .558 and r = .746, respectively for the same 2 groups). The peak of excretion of the three metabolites was found in urine samples collected the night after the spraying or leaf thinning operations.