Potassium, Rb and Sr contents and 87Sr/86Sr ratios of basalt glass are greatly modified during experimental alteration by seawater at temperatures of 150-300°C, water/rock mass ratios of 10-125, and 500 bar pressure. In all experiments K and Rb are leached from the rock in amounts which are a function of the temperature of interaction. The water/rock ratio, however, plays a less significant role in the mobility of K and Rb. In contrast, Sr is removed from seawater during interaction with basalt glass and enriched in calcic alteration phases. Concomitantly, interaction with seawater (87Sr/86Sr = 0.70920) increases the Sr isotopic composition of the glassy basalt, from an initial magmatic value of 87Sr/86Sr = 0.70260, to values of 87Sr/86Sr = 0.70512-0.70842. Strontium isotopic variation and trace element mobility documented during this investigation is similar, in many respects, to that inferred from studies of greenstones dredged from mid-ocean ridges, and metabasalts from ophiolites.