This study was conducted to elucidate the effects of different concentrations of strontium and its interaction with certain metals upon some physiological aspects of Phormidium fragile. The results revealed that dry weight, protein and carbohydrate contents as well as acid phosphatase activity decreased with increased strontium concentration. Low doses of strontium hardly affected lipids or DNA content as well as nitrate reductase and GOT activities. In the meantime, it increased GPT and alkaline phosphatase activities. Low concentrations of strontium decreased RNA content, but larger doses hardly affected its accumulation. Calcium nullified the harmful effects of strontium on dry weight, protein, carbohydrates and RNA contents but could not counteract strontium effects on the other parameters. Antimony hardly affected the influence of strontium on dry weight gain and DNA content, slightly decreased the carbohydrate content and alkaline phosphatase activity but slightly increased the protein content. Antimony nullified strontium effects on RNA or lipids levels, nitrate reductase, GOT, GPT and acid phosphatase activities. The addition of cadmium, singly or jointly with calcium and antimony to strontium-containing media as deleterious to all growth criteria. Pigment contents were severely attenuated by strontium alone or combined with other metals.