N-methyl-D-aspartate (NMDA)-receptor antagonists such as ketamine can induce transient schizophrenia-like symptoms and cognitive dysfunctions in healthy volunteers similar to those observed in patients with schizophrenia. Perceptual organization deficits have been documented in schizophrenia and are thought to be related to some symptoms associated with the illness. The current study was designed to determine whether people who repeatedly self-administer ketamine would also show deficits in perceptual organization. Using a psychophysically well-controlled measure of contour integration, we compared a group of recreational users (n = 16) to a group of poly-drug using controls (n = 16). Contour integration performance was measured on the night of drug use and 3 days later when drug free. The results showed that on the night of drug use, ketamine produced a dysfunction in contour integration however, this was not present 3 days later when drug free. Levels of dissociation were also higher in ketamine users only on the night of drug use. These preliminary data provide some support for the role of NMDA-receptor hypofunctioning in dysfunctional coordination of cognitive activity.