Waste biogas residual slurry (BRS) was used for the adsorption of Pb(II) from aqueous solution, over a range of initial metal ion concentrations (20-100 mg litre(-1)), agitation times (5-70 min), adsorbent doses (0.4-5.0 g litre(-1)) and initial pH values (1.5-6.0). The amount of Pb(II) adsorbed (mg g(-1) of adsorbent) increased with increases in the initial concentration of Pb(II). The applicability of the Lagergren rate equation was also investigated. The process of uptake of Pb(II) by BRS followed the Langmuir isotherm model and the adsorption capacity was 28 mg g(-1). An almost quantitative removal of Pb(II) from a solution (50 ml) containing 100 mg litre(-1) Pb(II) by 5.0 g litre(-1) adsorbent was observed at an initial pH of 2.5. Application of BRS for the effective removal of Pb(II) from radiator manufacturing industry wastewater has been demonstrated.