Some heavy metals namely, cadmium, copper, iron, nickle, lead and zinc and some organochlorine pesticide residues in water samples from Maekong River in Vientiane, Laos were investigated. Water samples were collected from 8 selected sites from the Maekong Rivers from Ban Narong, Muang Hatsaiphong to Ban May, Muang Srikhottabong. The samples were collected during two seasons in 1995 ; dry(May) and rainy(October) seasons in 1995. The heavy metal contents in the water samples were determined by atomic absorption spectrophotometry using an acetylene-air flame after preconcentration by extraction of the metal dithiocarbamate into the mixture consisting of methyl isobutyl ketone and cyclohexane followed ny back extraction into an aqueous phase prior to analysis. The average percentage recoveries of the added metal ions were in the range of 0-0.1, 1.4-10.0, 168.7-327.1, 0-7.2, 0-1.0 and 0-11.3 ppb for Cd, Cu, Fe, Ni, Pb and Zn respectively. Some organochlorine pesticide rescidues in the water samples from Maekong River were determine by gas liquid chromotography using an electron capture detector after appropriate sample pretreatment. It was found that beta-BHC, diedrin, edrin, and o,p’ –DDD

were not detected in both seasons. Other organochlorine pesticide residues were in the ranges of 0-0.5 ppb for alpha-BHC, 0-1.6 ppb for gammar-BHC, 0-0.3 ppb for delta-BHC, 0-0.7 ppb for o,p –DDT, 0-2.8 ppb for p.p’-DDT, 0-0.4 ppb for HCB and ppb for mirex. The organochlorine pesticide residues found in the dry season was higher than those found in the rainy season. There is no indication for heavy metal pollution but the pesticide residues are above the maximum allowable values recommanded by the Thai National Standard for surface water.