Cannabinoid assays were developed in response to the need for a simple, dependable, and cost-effective method for detecting the presence of cannabinoid metabolites in urine. Concerns about the widespread use of marijuana had increased the amount of cannabinoid testing being performed. This increase lead to a number of questions about passive inhalation of marijuana and the excretion patterns and retention times of cannabinoids. Some studies attempted to evaluate the potential effects of cannabinoid passive inhalation on individual’s claiming that a positive test for cannabinoids resulted from their unknowing inhalation of sidestream smoke released by a user. These claims, if true, could have a major impact on the interpretation and credibility of positive test results. It was concluded that it was possible, given sufficient time and intensity of passive marijuana smoke inhalation, that a person could produce detectable levels of urinary cannabinoids. However, it was extremely unlikely that anyone could unknowingly tolerate such an environment for the length of time necessary to absorb the required doses of THC. The remaining studies investigated the excretion patterns and retention times in first time, chronic, or regular cannabinoid users. It was concluded that excretion patterns and retention times were difficult to predict for a variety of reasons including individual metabolism, fluid intake, and frequency of urination.