The effect of welding fumes on ocular readaptation time (RAT) has been investigated. Objective measurements of RAT were obtained from a determination of the recovery time for optokinetic nystagmus following a bright flash of light. Welding electrodes of different types and chemical compositions were used. Welding fumes and the breathed gases were analyzed for particles, and the blood concentration of certain trace elements was determined. The results show that fumes from basic electrodes, containing high amounts of calcium and fluorides, and sometimes copper, produced a marked increase in RAT. The fumes from rutile electrodes, containing only low amounts of these substances, produced no demonstrable prolongation or RAT. Nor was RAT affected by the copper content of the electrodes. Thus the results appear to indicate that fluorides in the fumes produced by the basic electrodes cause the prolongation of RAT. The substances causing this prolongation seem to be bound to fume particles greater than 0.3 micron. Discomfort--nausea and headache--correlated with increased RAT prolongation. But analyses of the ambient air and of trace elements in the blood did not reveal any changes that could be correlated with the effect on RAT. RAT changes measured in conjunction with the inhalation of fumes from basic electrode welding are comparable to those seen after the intake of a therapeutic dose of oxazepam.