Scenedesmus obliquus cultures were subjected for 7 days to increasing levels of Cu+2 (1-60 μM). The cell number, dry weight, and chlorophyll content were reduced as the level of Cu+2 was raised. Photosynthetic oxygen evolution and respiratory oxygen uptake in the dark were also reduced, however, soluble protein contents were negatively affected by Cu+2. However, soluble carbohydrates and free amino acid content were variously increased by increased Cu+2 level. Free proline content was increased by up to 148% of that of the control, this being an indication of heavy metal stress.