Growth and ripening effects of Mon 0139 and 2139 and Polaris (glyphosine) were examined on sugarcane variety PR 980 in a field experiment on the north coast of Puerto Rico. The materials (Mon 0139 and 2139 at 0.1, 0.3, and 1.0 lb/acre and Polaris at 3.5 and 4.5 lb/acre were applied in December at the beginning of the harvest season, when environmental conditions were unfavorable for natural ripening. Mon 2139 at 10 lb/ acre applied 8 weeks prior to harvest gave significant increases in sucrose-percent- cane as compared to both Polaris and the control. There were no significant differences in performance between Mon 0139 and 2139, but both compounds gave increases in sucrose at 0.10 lb/acre, comparable to Polaris at the 3.5 lb/acre level. Phytotoxicity was evident at the 1.0 lb/acre rate of both compounds, and significant decreases in both growth and weight of cane tops were noted at this level. However, there was no residual growth suppression in the subsequent ratoon.