[en] This thesis described the determination of morphine like substances in human milk, poppy seed and rice by radioimmunoassay (RIA) and gas chromatography (GC). The first technique was implemented for human milk using chloroform extracts. Among the various drugs tested only codeine was found to have cross reaction with the antibody used and the method gave a sensitivity of 60 pg/tube or 300 pg/cm³. The coefficient of variation for both within and between assays were less than 8% whereas the percentage recovery of 10-25 ng/cm³ of standard morphine hydrochloride added into human milk was higher than 95%. Study in 4 hill tribe opium addicted women showed that the concentration of morphine like substances in their milk ranged from 0-250 ng/cm³. Poppy seed and rice were investigated by both GC and RIA. Poppy seed from four different sources were investigated for morphine and codeine. Over 1,200 ng of the compounds were detected in one gram of all the specimen studied and codeine was present in higher concentration. Determination with RIA gave a range of 2,000-6,200 ng in one gram of the seeds. No detectable amount of morphine or codeine was found with GC in either 4 samples of rice obtained from hill tribe villages or in one sample of low land rice whereas 0.4-2.5 ng/g were detected with RIA