Cannabis sativa grows abundantly among other natural vegetation in the northern part of Pakistan. Buffalo, the common dairy animals of the region, are allowed to graze upon this vegetation. These animals ingest significant amounts of marijuana, which after absorption is metabolized into a number of psychoactive agents which are ultimately excreted through the urine and milk. This potentially contaminated milk is used by the people of the region. Depending upon the amount of milk ingested and the degree of contamination, the milk could result in a low to moderate level of chronic exposure to Delta-9-Tetrahydrocannabinol (THC) and other metabolites especially among the children raised on this milk. This research was conducted to investigate the extent of passive consumption of marijuana by the consumers of potentially contaminated milk. Urine and milk specimens were obtained from buffalo and were analyzed for 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) which is a major metabolite for THC. The analysis was done by using gas chromatography/mass spectrometry. It was observed that during the months of June and July, 60 percent of the buffalo contained detectable levels of THC-COOH in their urine and 50 percent of these animals produced milk which was contaminated with THC or other metabolites. Analysis of the urine obtained from children with ages ranging from six months to 3 years, who were being raised on the milk from these animals, indicated that 29 percent of them had low levels of THC-COOH in their urine.(ABSTRACT TRUNCATED AT 250 WORDS)