Seventeen muscovites, eleven biotites, eleven microclines, one albite, and one lepidolite from five granite and granite pegmatite localities were analyzed for thallium, rubidium, and potassium by atomic absorption spectrophotometry. Rubidium and potassium were determined in aqueous solutions. Thallium was determined in butanol in which 0.1 gamma/ml T1 was easily detected. Mean Rb/Tl ratios range from 110 for pegmatitic biotites to 232 for granitic microclines. No significant difference in Rb/Tl ratios between granites and pegmatites was noted, while there is a tendency for T1 to be enriched, with respect to K and Rb, progressively in microcline, muscovite, biotite. Rubidium is similarly enriched with respect to K. Thallium content varied from 1 ppm in a microcline sample to 108 ppm in the lepidolite. Maximum value for microcline is 70 ppm, 54 ppm for muscovite and 37 ppm for biotite. Thallium appears to follow Kb more closely than K in granites and pegmatites. There is little variation in mean Kb/Tl ratios.