A school based study was undertaken to trace various sources of lead exposure in urban slum children. Two cases with elevated venous blood lead (PbB) levels were detected and confirmed in 100 consecutive Bombay school children, referred to a hospital school clinic for clinical pallor. A common source of lead exposure in one suburb, was implied by the significantly higher PbB levels here. Systematic family and environmental studies identified the source was a nearby factory manufacturing lead storage batteries. Similar studies for the other index case traced the source to the dust produced by small scale foundries and secondary lead smelters. This study indicates that large scale screening studies are necessary to establish the magnitude and epidemiology of this problem in Bombay.