1. The fatty acid composition of the triglycerides synthesized from sugar was determined in female Culex pipiens, a mosquito that overwinters in the adult stage.
2. The fat had approximately the same composition when synthesized at 5, 10, 20, or 30° C.
3. At each of these temperatures the fat composition was the same, whether a photo-period of 8 hr. or of 14 hr. was used.
4. The main fatty acids were palmitic (30%), palmitoleic (50%) and oleic acid (15%).
5. These results do not support a hypothesis that adipose tissue of poikilothermic animals synthesizes a more unsaturated fat under winter conditions.