The effect of temperature (T), relative humidity (RH), and growth stage (GS) of six field maize hybrids on the level of tolerance to rimsulfuron [N-((4,6-dimethoxypyrimidin-2-yl) aminocarbonyl)-3-(ethylsulfonyl)-2-pyridincsulfonamide] applied at 20, 40 and 60 g a.i ha -l were evaluated. The hybrids tested are adapted to three climatic zones of Quebec, Canada (zone 1: >2 700 maize heat units (CHU); zone 2: 2500 to 2 700 CHU; zone 3: 2 300 to 2 500 CHU).Two hybrids of each zone were considered. Three experiments were carried out under growth chamber and glasshouse conditions. Corn response to rimsulfuron doses was linear. Hybrids of zone 1 were more tolerant to rimsulfuron than hybrids from zones 2 and zone 3.Dry weight reduction of hybrids (DWR as a percentage of the untreated control 14 days after treatment) varied according to the dose from 22% to 29%, 31 % to 35%, and 36% to 38% in zones 1, 2, and 3, respectively. The response of maize hybrids to increasing temperaturewas linear, and the DWR was 12%, 28%, and 51 % at 14°C, 21 °C, and 28°C, respective1y. Injury to maize hybrids grown und er 60% and 75% RH averaged 31 % and 37% DWR, respectively. Corn plants treated at the 2- to 3-leaf growth stages showed, in general, more sensitivity to rimsulfuron than those treated at the 4- to 5- leaf stage. These results confirmthat both environmental conditions and maize genotypesplay an important role in the injury caused by rimsulfuron. Key words: herbicides, sulfonylurea, rimsulfuron, field maize hybrids, tolerance, environmental conditions. Abbreviations: CHU, maize heat units; T. temperature;RH, relative humidity; GS, growth stage; DWR, dry weightreduction.