Participants' expectations of marijuana effects are frequently cited as unmeasured post hoc explanations of variability in response to the drug, or of the data which fail to conform to the experimenters' expectations of the drug's effects. Twenty-four male volunteers, experienced in the use of marijuana, participated in research involving the administration of coltsfoot, placebo, and marijauna to investigate whether expectancy of marijuana effects could be measured and related to observed effects. Data for the Expectancy Questionnaire were derived from the Marihuana Effects Questions filled out when potential participants volunteered for the study and were compared to the High Questionnaire filled out after drug administration sessions. Expectancy was shown to have a quantifiable effect on the drug experience (both placebo and marijuana), even in an experimental situation. Prior frequency of occurrence of specific effects was positively related to both the intensity and duration of the effects in the laboratory. The data are discussed in terms of the learned components in getting stoned, and in terms of the social nature of cannabis intoxication.