Health complaints, blood pressure, sleep and sickness absence experience were studied in 308 female electronics workers employed for at least one year on 12 h shifts--253 on permanent and 55 on rotating schedules. Seventy-five 8 h day workers acted as controls. There were no significant differences in symptom prevalence between the controls and 12 h shift workers, except for complaints of tiredness, with a higher proportion of the rotating shift group also having headaches. No significant differences in prevalence of hypertension were noted. Although subjects on the night shift had shorter sleep than controls and 12h day workers, only the group on rotating schedule had a higher proportion of workers who did not sleep well compared to the controls. Sickness absence was not increased in the 12 h shift groups when compared to the controls. The results indicate no serious health problems among workers on 12 h shift for over a year.