As a pilot study of occupational stress and pregnancy, we measured urinary catecholamine excretion in ten pregnant physicians and three intensive care nurses between 26-37 weeks' gestation, once during a work day and again during a non-work day. Urinary catecholamines were increased by 58% (P less than .03) during work periods compared with non-work periods. Catecholamine levels were also increased by 64% (P less than .025) over those of a working non-physician control group of similar gestational age. Urinary catecholamine levels are a direct reflection of plasma catecholamine levels. Catecholamine levels are known to increase with physical stress, such as standing, and with mental stress, such as difficult problem-solving. Catecholamines are also known to decrease uterine blood flow. Measurement of catecholamines may be a helpful marker in investigating the relationship between occupation and pregnancy outcome.