Cells of Desmodesmus subspicatus 54.80 were used to examine the toxicity of copper sulphate (CuSO4.7H(2)O). The experiments were performed according to OECD 201 standard procedures (International Organization for Standardization; 1984). Parameters measured were the number of cells as well as chlorophyll-a, intracellular and extracellular Cu contents. The number of cells and chlorophyll-a content decreased from 58.000 to 22.667 cells ml(-1) and from 0.993 to 0.331 mg L-1, with increasing Cu concentrations, respectively. The 96-h EC50 value for D. subspicatus determined was 2.447 mg L-1 Cu. Intracellular copper increased from 9.626 to 67.793 x 10(-4) ng Cu per cell whereas extracellular copper increased from 7.011 to 138.233 10(-4) ng Cu per cell of D. subspicatus exposed to 1 and 5 mg Cu L-1.