A feasibility study on the potential use of three bacterial test systems on the toxicity screening of zinc is presented. In this investigation, the toxicity screening procedures included, were the Microtox test using a luminescent halophyte bacterial strain, Photobacterium phosphoreum, a motility test employing Spirillum volutans, and a growth zone inhibition test using Bacillus cereus as the test organism. The EC, , value of zinc has been found to be 1.35 mg/L with the Microtox test under optimum test conditions (T150ct15m,n). However, the toxic response of zinc wassignificantly dependent upon the test temperature and incubation time. It decreased at higher temperatures and increased with longer incubation periods. In the case of the motility test, the minimum effective concentration (90%) value of zinc was 3.00 mg/L at optimum assay conditions (T280ct60m,n) while the toxicity of zinc in the growth zone inhibition procedure was found to be 2.25 mg/L at 30Β°C after 18 h incubation. Overall, the study showed that the Microtox test was the most sensitive screening procedure followed by the growth zone inhibition test, and the motility test was least sensitive among the three test systems. The growth zone inhibition procedure was the simplest of all the systems. 0