Relationships between occupation, working conditions, and the development and outcome of pregnancy were analysed on a sample of women employed in hospital during their pregnancy. Ancillary staff members experienced more uterine contractions during pregnancy, more preterm deliveries, and more low birthweight infants than those performing other duties; this remained true after adjusting for social characteristics. The rate of preterm delivery was significantly higher in the presence of at least two of the following arduous working conditions: stand-up work, carrying heavy loads (exclusive of patients), and heavy cleaning tasks; this was so, whatever the occupation.