Thermal responses and muscular activity in repetitive work were studied in eight women and eight men at 19 degrees C (thermoneutral) and at 4 degrees C (cold). Furthermore, effect of a heating vest was studied at 4 degrees C. Women had lower (p < 0.05) mean skin temperature compared with men at each thermal condition. Muscular activity (microV) was generally higher in women compared with men, being significantly higher in m. deltoideus (p < 0.05). Women had lower (p < 0.01) maximal isometric strength compared with men, which may have influenced the observed higher muscular activity during work in women. However, compared with thermoneutral, working in cold increased (p < 0.05) muscular activity in the forearm and upper arm extensors only in men. The vest did not significantly counteract the increase in muscular activity. In conclusion, sex differences should be considered when evaluating cold protection and work load reduction in repetitive work in cold environments. Present results indicate that in identical work, sex affects thermal responses and muscular activity during repetitive work in conditions comparable with cooled departments in the food-processing industry. Sex differences should be considered when evaluating cold protection and preventive measures for work load reduction.