As part of a longitudinal study of the cause of carpal tunnel syndrome in industry, we evaluated sensory conduction of the median nerve in relation to age, gender, hand dominance, occupational hand use, and clinical diagnosis. The original 1984 study group consisted of 942 hands of 471 industrial workers, and the follow-up study group in 1989 consisted of 630 hands of 316 (67%) of these same workers. The palmar segmental stimulation technique was employed, and slowing was defined as a maximum latency difference of 0.4 msec or more after adjustment for temperature variation. There was no significant change in the prevalence of slowing between 1984 and 1989 (23% in 1984, 22% in 1989), and slowing was still strongly correlated with increased age but not with gender. Slowing continued to be more prevalent in the dominant hand. Slowing was no longer correlated in any fashion with occupational hand use. The prevalence of probable carpal tunnel syndrome was still strongly correlated with the degree of slowing. Age and hand dominance were more important than any job-related factor in the prediction of slowing after 5 years.