Thylakoids isolated from the purple bacterium Rhodopseudomonas spheroides were examined with regard to the amino acid composition of their structural proteid and the fatty acid composition of their ether soluble lipids. The fatty acid composition was nearly identical with that of the ether soluble lipids from whole cells. The main component was cis-vaccenic acid. Mono-unsaturated and saturated fatty acids with 18 and 16 C-atoms were dominating. After extraction of the lipids and washing of the thylakoids with NaCl and NaOH solutions, there remained at least two protein fractions and these could be separated by phenol-water at 65 °C. The amino acid composition of the structural proteid was similar to that of the structural proteids from thylakoids of Oscillatoria, Chlorella and green higher plants.