Glasshouse studies were undertaken to determine the effect of imposed moisture stress on the phytotoxicity of haloxyfop; the absorption, translocation, and metabolism of 14C-haloxyfop; and 14C-photoassimilate partitioning in johnsongrass and large crabgrass. Following foliar applications of haloxyfop at 30 and 25 g ai ha–1 to large crabgrass and johnsongrass, respectively, control 15 days after treatment was 92% for nonstressed plants and less than 12% for water-stressed plants. Foliar absorption of 14C-haloxyfop was reduced by moisture stress 1, 3, 5, and 24 h after treatment (HAT) in large crabgrass and 1, 3, 5, 48, and 72 HAT in johnsongrass. Regardless of stress treatment, absorption in both species reached a maximum by 24 HAT. Translocation of the radiolabel from the treated leaf to plant parts above and below the node of the treated leaf was inhibited by moisture stress in large crabgrass and johnsongrass at all harvest intervals beginning 5 and 24 HAT, respectively. Metabolism of 14C-haloxyfop was not altered by moisture stress. Fixation of 14CO2 and subsequent distribution of the 14C-photoassimilates were reduced by moisture stress. Decreases in photoassimilate translocation were similar to reductions in 14C-haloxyfop translocation. Moisture stress reduced the phytotoxicity of haloxyfop in the two grasses, and the reduced activity of haloxyfop appeared to be partially related to changes in herbicide absorption and translocation.