The objective of the study was to assess whether moderate occupational exposure to lead may be associated with early changes in potential target organs (thyroid, testes, kidney, autonomic nervous system). Workers exposed to lead in a lead acid battery factory (n = 98; mean blood lead 51 micrograms/dl, range 40-75 micrograms/dl) and 85 control workers were examined. None of the indicators of kidney function (in urine: retinol-binding protein, beta 2-microglobulin, albumin, N-acetyl-beta-D-glucosaminidase; in serum: creatinine, beta 2-microglobulin), endocrine function (follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, thyroxine, triiodothyronine) and autonomic nervous system (R-R interval variations on the electrocardiogram) were correlated with lead exposure (blood lead or duration of exposure) or showed significantly different mean values between the exposed group and controls. These results and an assessment of the published data suggest that compliance with the Directive of the Council of the European Communities on lead exposure (health surveillance in workers whose lead in blood exceeds 40 micrograms/dl and removal from exposure when blood lead exceeds 70-80 micrograms/dl) would prevent the occurrence of significant biological changes in the majority of lead-exposed workers.