Laboratory technicians working with plunger-operated pipettes have a monotonous work task loading the arm. A study was performed to evaluate the prevalence of hand and shoulder ailments among laboratory technicians in relation to the 'dose' of pipetting and relation to some psychosocial factors was used to compare a cohort of 128 females employed by university research laboratories with reference data obtained from 25 378 female Swedish state employees in general. The prevalence of hand ailments among the laboratory assistants was found to be twice that among female state employees in general. In the cohort a nested case-control study indicated that an increased risk of hand (OR = 5, 0) and shoulder (OR = 2, 4) ailments was associated with more than 300 h/year pipetting. Suggestions for permissible exposure levels for pipetting are presented.