Occupational factors in spontaneous abortion were studied in the current and previous pregnancies of 56,013 women interviewed in 11 Montreal maternity departments, 1988 to 1984. Ratios of observed to expected abortions (BR), after allowance for nonoccupational confounders, were significantly increased (P< .05) among nursing assistants and attendants (RR 1.24 in current and 1.13 in previous pregnancies), food and beverage servers (RR 1.31 in current and 1.11 in previous pregnancies) and sales persons (RR 1.18 in current and 1.18 in previous pregnancies). Women whose work entailed heavy lifting, other physical effort, long hours, exposure to noise, and exposure to cold had also significantly increased risk ratios. However, when occupational groups were ranked according to work demands, thus avoiding potential bias from prior knowledge of outcome, increased risks were associated consistently only with heavy lifting and other physical effort.