Exposure of Cd to hepatic enzyme activity, viz. acid‐ and alkaline phosphatases, catalase and glucose‐6‐phosphatase of tilapia, Sarotherodon mossambicus, affected most of the aforementioned enzymes. Acid phosphatase and catalase activities were increased in the liver while that of glucose‐6‐phosphatase decreased by almost as much as fifty percent with 1.0 mg 1‐1 of Cd. In contrast, the additional increase in Cd concentration did not decrease glucose‐6‐phosphatase activity any further. At cellular level, Cd exposure at a lethal dose of 3.5 mg 1‐1 increased lysomal activity in liver cells. Large numbers of lysosomes at various stages of activity were also evident. Primary lysosomes which are smaller in size containing lysosomal enzymes, but not having received substrates, can be easily distinguished from the larger secondary lysosomes in which substrates undergo enzymatic attack. Further, depletion of both fats and glycogen reserves were also noticeable. The mitochondria were found to contain much more intr...