Controversy surrounds the question of whether there are dopamine (DA) receptor abnormalities in the brains of schizophrenia patients; in particular, whether DA receptors of the D2 family are elevated in density. Methodological factors and sample characteristics have been postulated to account for differences in study outcome, but there has been no systematic analysis of the contribution of these factors to study effect sizes. This meta-analysis of the research findings sought to determine the influence of methodologic factors and sample characteristics on the magnitude of diagnostic group differences in DA D2 density (Bmax) and affinity (Kd). The analysis suggests at least moderate effects, such that schizophrenia patients show an elevation in both values when compared to controls. These effects are amplified in medicated patients, but not solely attributable to antipsychotics. The group differences in DA D2 receptor density and affinity increase with age among nonmedicated patients. The use of a butyrophenone ligand also yields larger effects. It is concluded that a subgroup of schizophrenia patients manifests increased DA D2 receptor density and decreased receptor affinity. In the absence of medication, these changes may become more pronounced with age. Differences in study outcome are also partially due to methodologic factors, including the ligand.