The concentrations of common Pb in the Atlantic Ocean and Mediterranean Sea were investigated. Samples of rural snow were also analyzed in attempts to validate the view that the oceans have been contaminated by lead tetraethyl aerosols. The concentration of 0.01 N HCl acid-soluble Pb in snow was about 2 mu g Pb/kg snow. The isotopic composition of Pb from snow was found to be: Pb/ sup 206//Pb/sup 204/ = 18.01; Pb/sup 206//Pb/sup 207/ = 1.144 and Pb/sup 206//Pb/ sup 207/ = 0.469 The concentr ation of Pb measured in snow was found to be 10 to 100 times as large as that measured in sea water. In general, Pb concentrations at the Atlantic stations appear to increase from surface to intermediate or deep waters, and then decrease again in very deep or bottom waters. Common Pb concentrations in Central North Atlantic surface waters are about 0.05 mu g/l. Values in offshore surface waters increase to 0.09 mu g/l near Morocco and to 0.2 mu g/l in the Mediterranean. (P.C.H.)