Cannabinoid acids readily decarboxylate to the corresponding cannabinoid. Methods are available for the determination of delta 9-tetrahydrocannabinol (THC) and its acids (THCA) and published data on the levels of these compounds in cannabis are summarized. Using gas and liquid chromatography, fresh cannabis (64 samples) and cannabis resin (26 samples) from different countries were examined. Wide variations in the relative amounts of THCA and THC in cannabis were found. For cannabis resin, a wide range of values was also found (0.5: 1 to 6.1: 1), the lower values being in resins from the Indian sub-continent and the higher values in resins from the Mediterranean area. Total THC values were in the range 1.0 - 10.6% in cannabis and 6.0 - 12.5% in cannabis resin.