1. 1. This study evaluates several possible incubation systems which might be applied to future tcratogenic investigations. 2. 2. Rabbit embryos were removed at 12 and 14 days after copulation and incubated in vitro with [1- 14C]acetate under a variety of conditions. 3. 3. Following incubation, the lipids were extracted, separated into two major classes, and assayed for 14C. 4. 4. Twelve- and 14-day rabbit embryos synthesized lipids rapidly from acetate. 5. 5. The extent of acetate incorporation was dependent upon incubation time and substrate concentration, but not upon small differences in tissue weight. 6. 6. The distribution of 14C activity between neutral lipids and phospholipids was partially dependent upon substrate concentration. 7. 7. Acetate incorporation was greater when whole embryos were incubated in Hanks's solution or when fragmented embryos were incubated in TC-199 than when whole embryos were incubated in TC-199 or TC-199 plus serum.