In order to investigate the genotoxic effects of occu-PBLs the proliferative rate index (PRI) was already pational acrylonitrile (ACN) and dimethylform-increased in month 0 compared with the controls. amide (DMF) exposures, clinical serum and urine In each study, significant increases in CA and SCE parameters and genotoxicological endpoints such frequencies, as well as increases in UDS were found as chromosome aberration (CA), sister chromatid in PBLs of the exposed subjects. The frequencies of exchange (SCE), high frequency SCE (HFC), cell chromatid breaks and acentric fragments further incycle kinetics, and UV-induced unscheduled DNA creased in month 7 and remained constantly elesynthesis (UDS) were followed up three times during vated in month 20. Increased yields of both chromaa 20-month period in peripheral blood lymphocytes tid and chromosome-type exchange aberrations first (PBL) of 26 workers (13 maintainers and 13 fiber appeared in month 20, when HFCs were 2.72 times producers) occupationally exposed to ANC and/or more frequent in fiber producers than in maintainers. DMF in a viscose rayon plant, 26 matched control The role of some important biological confounding subjects, and six industrial controls (all males). Six factors (age, white blood cell count, and hematocrit) of the 26 exposed subjects were hospitalized be-and lifestyle confounding factors (smoking and drinkcause of liver dysfunction that had developed due ing habits) were subjected to an analysis of variance to inhalative DMF exposure. The rate of smoking during the second study. Increased CA, SCE, and was estimated on the basis of serum thiocyanate UDS were found both in control and exposed smok-(SCN) levels. Average peak air ACN and DMF con-ers when current smoking was established on the centrations were over the maximum concentration basis of the serum SCN levels. The cytogenetic data limits at the time of both investigations. Urine ACN suggest that occupational exposures to ACN and and monomethyl-formamide (MMF) excretions of DMF induce considerable genotoxic consequences the exposed subjects were almost doubled after and may increase the cancer risk in the exposed work shifts. An increase in lymphocyte count (in human populations. Environ. Mol. Mutagen. months 0 and 7), and severe alterations in the liver 31: 301 -310, 1998 ᭧ 1998 Wiley-Liss, Inc. function were observed in the exposed subjects. In