Lead was determined in 13 U.S. Geological Survey standard rocks by graphite furnace atomization and atomic-absorption spectrometry after extraction of lead with diethylammonium diethyldithiocarbamic acid. An analysis of variance of the results obtained from a random sampling of three different bottles of each standard rock showed no heterogeneity among bottles, at the F(0.95) level, for a 100-mg sample-size. The relative error of the method, based on the standard deviation of the mean within bottles, was generally less than 10%.