Lead isotopic composition and uranium and lead concentrations have been determined for galena, sphalerite, pyrite and acetic acid soluble material from the McArthur area in order to test the hypothesis of a dual sulphur source suggested by the sulphur isotope data of Smith and Croxford (Sulphur isotope ratios in the McArthur lead-zinc-silver deposit, Nature Phys. Sci. 245, 10-12 (1973)). Galena, sphalerite and the acetic acid washes from the McArthur deposit have uniform isotopic ratios (206Pb/204Pb, 16.07-16.15; 207Pb/204Pb, 15.37-15.47; 208Pb/204Pb, 35.57-35.89) consistent with other conformable ore deposits, whereas the ratios for pyrite are variable and quite radiogenic (206Pb/204Pb, 16.24-16.49; 207Pb/204Pb, 15.42-15.58; 208Pb/204Pb, 35.82-36.98). Acid washes where dolomite is a major dissolved phase are also radiogenic. The lead in the pyrite appears to have been derived from at least two sources: the less radiogenic lead coming from an exhalative source as for galena and sphalerite and the more radiogenic lead probably being leached from the country rocks. It is proposed that analysis of pyrite for isotopic composition and concentration of lead could be used as an indicator for similar types of deposits in this area.