This study of nurses' risk of selected chronic diseases in the context of potential biological exposure compares the health status of nurses to that of their female siblings. Self-report questionnaires distributed to each participating nurse were administered to an historical cohort of 491 female nurses aged > or =50 years. Questionnaires covered work and health history of the nurses and the control group of 232 of their age-matched female siblings. We developed a semiquantitative exposure matrix based on workplaces to describe biological exposure. Risk for coronary heart diseases, high blood pressure, dislipidemia, and thyroid and liver disease was significantly higher among the nurses compared to the controls. Total cancer and diabetes risks were similar for both groups. Cumulative biological exposure was associated with liver disease. Employment as a nurse may pose a risk for cardiovascular, thyroid and liver diseases. The specific determinants of this increased risk warrant further investigation.