The effect of divalent metal cations (Cd 2 + , Cu 2 + , Zn 2 + , Fe 2 + , Co 2 + ) on nitrate uptake and the effect of Cd 2 + on nitrogen and sulphur assimilation enzymes were studied in the eukaryotic alga Chlamydomonas reinhardtii. Nitrate consumption was not inhibited by metal concentrations below 100<space>μM; however, concentrations exceeding 150<space>μM Cd 2 + , Cu 2 + or Zn 2 + induced 75<space>% inhibition, whereas Fe 2 + or Co 2 + did not significantly affect nitrate uptake. Among the enzymes of nitrogen and sulphur assimilatory pathways, 2-d exposure of C. reinhardtii cells to 100<space>μM Cd 2 + did not affect ferredoxin-nitrite reductase (EC 1.7.7.1), ferredoxin-glutamate synthase (EC 1.4.7.1), NADH-glutamate synthase (EC 1.4.1.14) and O-acetyl-L-serine(thiol)lyase (EC 4.2.99.8) activities, but a 45<space>% inhibition of glutamine synthetase activity (EC 6.3.1.2) was observed. This inhibition increased with Cd 2 + concentration and was reverted by adding Mn 2 + to the reaction mixture, which can be interpreted as the result of a competitive inhibition of Mn 2 + in glutamine synthetase by high cadmium concentration.