Published reports examining the efficacy of fish oil for preserving renal function in immunoglobulin A (IgA) nephropathy have yielded conflicting results. This investigation was a meta-analysis conducted to determine whether the medical literature supports this therapy. In addition, the sources of variability among published findings were examined. Studies were combined using a random effects model. Five controlled studies were identified, two with positive results and three with negative results. Forty-four percent of the between-study variance could be attributed to differences in follow-up times and, less significantly, the number of renal function measurements; a weighting procedure was developed, eliminating this variance from the combined result. When all studies were combined, the mean effect, +0.25 +/- 0.23 SD (positive effects indicate that treatment was superior to control), was not statistically significant; however, the probability of at least a minor beneficial effect was 75%. Mixed-effects regression suggested that this therapy may be more effective among individuals with more proteinuria. The medical literature, therefore, does not prove the efficacy of fish oil therapy in IgA nephropathy, but suggests that an additional placebo-controlled trial is warranted. A sample-size calculation indicated that such a trial should be larger than those to date or should attempt to increase the treatment effect, perhaps by treating for more than 2 yr or enrolling more severely proteinuric individuals.