The evolution of occupationally induced color vision loss was studied in workers exposed to various chemicals. Exposure was evaluated by biological monitoring or personal air samplers, and color vision using the Lanthony D-15 desaturated panel (D-15 d). The effect of short-term interruption of exposure was studied in 39 Styrene (St) exposed workers: at a first examination a dose-related color vision loss was disclosed; a re-test performed after one month's interruption of exposure did not show any improvement of the effect. The evolution during longer periods was studied in another group of 30 St workers. Exposure and color vision were evaluated, then a follow-up was done 12 months later: the exposure was unmodified or slightly decreased in 20 subjects, and D-15 d outcomes remained unchanged, while St levels had increased and color vision loss progressed in the other 10. Similar results were obtained in 33 PCE exposed dry-cleaners: no change in color perception was observed in 14 workers whose exposure decreased, while in the other 19 a rise in PCE levels was followed by a significant color vision worsening. In 21 Hg exposed workers whose mean urinary excretion of Hg was threefold the BEI proposed by ACGIH, a dose-related impairment in color perception was observed. 12 months after a marked reduction of exposure, an almost complete recovery of the impairment was observed. Our data show that an increase in exposure can induce a worsening in color vision loss. A short interruption in exposure did not reduce the effect. A more prolonged reduction of dose reversed color vision loss in Hg exposed workers, while in solvent-exposed individuals the progression deserves further evaluation. D-15 d proved a useful test for studies on the evolution of color perception in workers exposed to eye-toxic chemicals.