1. Different initial affective responses occurred in identical twins under the influence of d-LSD-25 and psilocybin.2. These affective displays were related to the differences in personality between the twins.3. It was possible for the affectivity of each twin to influence the affective response of the other at various times during the studies.4. This communication of affect substantiates the hypothesis that affective responses associated with hallucinogen administration are personality specific rather than drug specific(1, 2, 3, 4, 5).5. The drug specific changes in the autonomic, proprioceptive and perceptual spheres were similar in both twins and not modified to any noticeable extent by environmental influences.6. Because of their profound effects, hallucinogens should be restricted to research use exclusively in a hospital setting. In our opinion, their use at this time for any other purpose or in any other setting is dangerous.Abstract Teaser