In this study initial data were generated to develop laboratory control charts for aquatic toxicity testing using the nematode Caenorhabditis elegans. Tests were performed using two reference toxicants: CdCl₂ and CuCl₂. All tests were performed for 24 h without a food source and for 48 h with a food source in a commonly used nematode aquatic medium. Each test was replicated 6 times with each replicate having 6 wells per concentration with 10±1 worms per well. Probit analysis was used to estimate LC₅₀ values for each test. The data were used to construct a mean (¯x) laboratory control chart for each reference toxicant. The coefficient of variation (CV) for three of the four reference toxicant tests was less than 20%, which demonstrates an excellent degree of reproducibility. These CV values are well within suggested standards for determination of organism sensitivity and overall test system credibility. A standardized procedure for performing 24 h and 48 h aquatic toxicity studies with C. elegans is proposed.