Budgets of Ca++, Mg++, Na+, and K+were determined for alevins of Atlantic salmon Salmo salar incubated at pH 6.8, 5.1, or 4.5. Accumulation of Ca++, K+, and Na+by larvae was reduced at pH 4.5 whereas Mg++accumulation was unaffected. The extrapolated dry weight of larvae at terminal yolk resorption was reduced from 27 mg at pH 6.8 and 5.1 to 20 mg at pH 4.5. The findings support the hypothesis that high acidity affects ion uptake from the ambient water more than yolk-to-larva transfer of cations.