This paper reviews the debate over the evidence for ESP provided by experiments using the ganzfeld technique, a simple method used to induce a mild altered state of consciousness. The quantitative literature review technique called meta-analysis has played a prominent role in this controversy. The first question addressed by the reviewer is whether the data establish that ESP in the ganzfeld is replicable. Issues discussed include the effect of multiple analyses, the 'file-drawer' problem and statistical errors. The second question asks, (...) if the effect is real, can it be explained by methodological artifacts? Potential flaws discussed include sensory leakage, problems of randomization and participant fraud. The reviewer's first conclusion is that the aggregate database does provide evidence for a genuine psi effect. However, heterogeneity of results across experimenters indicates that the phenomenon is not easily replicable. The second conclusion is that conventional alternative explanations offered for the observed results tend to be conceivable, but even critics sometimes agree that they are implausible. (shrink)