A longitudinal study of employment patterns and turnover of clinical laboratory personnel in the Minneapolis-St. Paul area was conducted for the years 1970, 1980, and 1990. Laboratory staffing patterns for the years studied showed a general plateau in numbers and categories of personnel between 1980 and 1990, following a doubling in those numbers between 1970 and 1980. In 1990, for a geographic area of 2.2 million people, a total of 2,500 laboratory personnel were employed in 31 major laboratories. Fifty-six percent were medical technologists (clinical laboratory scientists), 6% cytotechnologists and histologic technicians, 23% laboratory technicians, 9% phlebotomists, and 7% in "other" categories. The ratio of full- to part-time employees was approximately 3 to 1. Between 1970 and 1990, annual turnover rates for all laboratory personnel declined from 20% to 15%. In 1990, the personnel group experiencing the lowest turnover was in cytotechnology (4%) and the rate for medical technologists was 9%. The turnover for laboratory technicians was 17%, and the rate for histologic technicians was 19%. Highest turnover occurred among phlebotomists (36%) and "others" (39%). While the numbers of laboratory personnel employed leveled off between 1980 and 1990, numbers of new graduate technologists and technicians decreased by approximately one-half. Personnel shortages in laboratory science can therefore be expected to continue.