Because of the high incidence of viral hepatitis among our laboratory staff, a study was undertaken to evaluate aerosol production associated with a number of clinical laboratory procedures. To do this, we employed a coliphage and technetium m99 as tracers. It was found that procedures involving the shaking of a specimen within a confined space resulted in abundant aerosol production, while other procedures produced relatively little. Of significance was the considerable bench-top and instrument-surface contamination associated with all procedures.