The net thoracic magnetic moment of 58 highly exposed nonsmoking shipyard welders and 13 unexposed nonsmoking electricians was measured with an alternating current susceptibility bridge. The welding cohort exhibits a thorax magnetic moment, which on the average is less diamagnetic than that of the controls. This shift is consistent with a median lung burden of 110 mg Fe3O4, or 220 mg of the welding fumes characteristic for shipyard exposures. Among welders with 5+ yr of exposure, there is a slight but statistically significant correlation (r = 0.49) (p less than .0001) between inferred lung burden and lifetime occupational exposure. Although chronic bronchitis incidence and average lung function parameter values of the welders are different from those of the nonexposed cohort, respiratory status does not correlate further with either self-reported exposure or measured lung retention.