IN ORDER TO STUDY THE EFFECT OF METRIBUZIN ON THE WEEDS OF WHEAT FIELDS, TWO EXPERIMENTS WERE CONDUCTED IN AN EXPERIMENTAL FIELD AT IRANIAN RESEARCH INSTITUTE OF PLANT PROTECTION IN 2006 AND 2007. TREATMENTS WERE IN A FACTORIAL ARRANGEMENT AS A RANDOMIZED COMPLETE BLOCK DESIGN WITH FOUR REPLICATIONS. THE FACTORS INVESTIGATED IN FIRST YEAR WERE – THREE WHEAT VARIETIES: SHIRAZ, PISHTAZ AND M-79-6 LINE; METRIBUZIN DOSAGES: 1.0, 0.75, 0.5 AND 0.0 KG HA-1; HERBICIDE APPLICATION TIMING: PREPLANT AND SOIL INCORPORATED AND POST EMERGENCE AT THREE TO FOUR- LEAF GROWTH STAGE OF WHEAT. THE FACTORS INVESTIGATED IN SECOND YEAR WERE THREE PLANT DENSITIES 400, 500 AND 600 PLANT M-2 AND METRIBUZIN AT 0.0, 0.2, 0.4, 0.6 AND 0.8 KG.HA-1. RESULTS SHOWED THAT APPLICATION OF 1 KG.HA-1 METRIBUZIN IN FIRST YEAR AND APPLICATION OF METRIBUZIN AT 0.6 OR 0.8 KG.HA-1 DENSITIES OF 500 OR 600 WHEAT PLANT M-2 RESULTED IN THE HIGHEST REDUCTION OF TOTAL DRY MATER OF WEED IN SECOND YEAR. THE HIGHEST GRAIN YIELD WAS OBTAINED USING 0.6 KG HA-1 AND 500 PLANTS M-2. WEED CONTROL AT THIS RATE OF HERBICIDE APPLICATION MIGHT BE SUITABLE AND FROM ENVIRONMENTAL STAND POINT USING HIGHER RATE IS STRONGLY NOT RECOMMENDED.