A joint effort to evaluate a battery of bioassays for regulatory purposes was conducted as an intercalibration exercise by institutions in eight countries (Argentina, Canada, Chile, Colombia, Costa Rica, India, Mexico, and Ukraine) with support from the International Development Research Centre (IDRC). The precision of the tests carried out in the Colombian Laboratory was evaluated by comparing the results obtained with the reference toxicants used as positive controls, as well as with a set of five blind samples which in fact had the same toxicant concentration (metolachlor plus cadmium). The coefficients of variation (CV) obtained with each bioassay for the positive controls ranged from 5 to 21% except for the Panagrellus test which gave CVs as high as 67%. The 100% sample concentration results of the mixture (metolachlor/cadmium) showed CVs between 2 and 55%. The highest value was again obtained with Panagrellus and the lowest value with the root elongation test. Even though the Panagrellus test had previously been used in our laboratory, its extra requirements in terms of time and training could be the reason for the high variability. The results also showed that the most sensitive test for heavy metals and pesticides was the Daphnia test. Hydra and Panagrellus tests showed the highest sensitivity response for the organics evaluated. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 297–303, 2000