A study was undertaken to examine the growth of normal and 5-fluorouracil-treated quail secondary palate during embryogenesis. The rates of DNA, RNA, and protein synthesis were measured in the developing quail palate by liquid scintillation counting of radiolabelled thymidine, uridine, or leucine. In addition, shelf volume was determined morphometrically. The results showed that in control palates the shelf volume increased rapidly between days 5 and 7 of incubation. Drug treatment on day 4 did not alter the shelf volume until day 9 of incubation, at which time the treated shelves were smaller than controls. In control palates, the rate of DNA synthesis decreased steadily between days 5 and 9 of incubation. A burst in RNA synthesis on day 7 of incubation was followed by an increase in protein synthesis. Administration of FU seems to exert its effect via disturbing the synthesis of RNA and protein, instead of disruption of DNA synthesis, to ultimately affect the shelf area, and thus palate morphogenesis in quail. Comparison of avian and mammalian data indicated that differences in their palate morphogenesis are also reflected in the different temporal patterns of various macromolecular synthesis.