The use of mercuric chloride as an histological fixative was associated with high environmental atmospheric concentrations of mercury vapour (up to 0-5 nmol/l) as well as mercury compounds (total Hg to 1-0 nmol/l). Technicians exposed to this environment showed increased urinary mercury (median value 265 nmol/24h) and protein outputs (median value 117 mg protein/24h). Routine control measures, ventilation and careful handling of mercuric chloride solutions, reduced the level of atmospheric mercury vapour levels to within acceptable limits (threshold limit values 0-01 mg/m3 (0-05 nmol/l) alkul compounds and 0-05 mg/m3 (0-25 nmol/l) for all forms except alkyl). This reduction was associated with the disappearance of trace proteinuria from the technicians' urine. Contamination of histology laboratories by mercuric chloride should be minimised.