A field study was conducted to assess cardiorespiratory and musculoskeletal stress and strain and work output during manual sorting of postal parcels, and to detect the effects of parcel sorting on the maximal muscle strength and endurance. The volunteer subjects comprised 32 healthy male sorters with mean (+/- s.d.) age of 34 +/- 7 years at five different sorting sites. Each subject was studied during one evening work shift. During the shift of 391 +/- 46 min the subjects manually sorted 1173 +/- 630 parcels and walked 4.7 +/- 2.3 km with and without the load. While sorting, heart rate was 101 +/- 18 beats min-1. In the heaviest tasks the oxygen consumption was 1.2 +/- 0.41 min-1, and no elevated blood lactate concentrations were found. Work postures in which the back was bent forward averaged 24% of the time for sorting. The overall cardiorespiratory rating and local ratings of perceived exertion for arms, back, and legs did not exceed the 'somewhat strong' level during the work shift. The maximal static strength both for the right and left hand-grip muscles was, on average, 3% lower (p less than 0.05) after the work shift than before the shift. No significant differences were found in the static or dynamic endurance times for the hand-grip muscles when the results obtained after the work shift were compared to the baseline values. At sorting centres the stress and strain on the cardiorespiratory and musculoskeletal system was evaluated to remain within acceptable limits for healthy male sorters.