Three cassava cultivars, Serralles, Sta. Catarina, and Zenon, were field evaluated at nine and 12 months after planting for root tuber yield and hydrocyanic acid potential (HCN-p) on an Oxisol at the ARS Farm, Isabela, Puerto Rico, during 1993-94. Significant differences were found in root tuber yield and HCN-p among cvs. and also in replication x cv. and HCN-p for replications and harvest dates. Sta. Catarina cv. averaged the highest root tuber yield with 31.9 tons/ha, while the Zenon cv. had the lowest HCN-p, 39.1 ppm. Across cvs., there was no significant difference between the two harvest dates in terms of root tuber yield; however, the root tuber HCN-p was significantly lower at the nine-month harvest (45.6 ppm). According to the findings of a taste-testing panel, the root tubers of all three cvs. at the two harv est dates had good culinary quality. However, at nine months, root tubers of the Zenon cv. were considered superior to the other two cvs.; while, at 12 months, those of the Sta. Catarina cv. were slightly preferred by the panel.