Acid rain produced by atmospheric pollution may decrease the pH value of water and increase the availability and potential toxicity of metals in water which have detrimental effects on aquatic organism, including algae, the important component of the primary production, and, thus, the entire aquatic food chain. Recent reviews of the effects of acid rain on freshwater ecosystems have emphasized research interest in soluble trivalent aluminum, although Al is rated low among trace metals in biological importance. On the other hand, zinc is an important trace element for the growth of phytoplankton and the cofactor of some enzymes. The growth response and tolerance of different species of algae to Al and Zn have been reported by Whitton who showed that algal growth would be stimulated by lower levels of the metals and totally inhibited by higher levels. These is little information, however, on the effect of Al on biochemical processes in aquatic organisms. This study investigates the influence of aluminum and zinc on several physioclogical processes in S. capricournutum, a common species of green algal in lake water. Algal growth (dry weight), ATP levels and the activities of several enzymes in the algal cells were measured after the treatment withmore » various concentrations of Al and Zn in culture medium. Special attention is given to the relation between the enzymatic response and algal growth. 15 refs., 2 figs., 1 tab.« less