1. Cell walls of Pseudomonas aeruginosa were prepared and analysed. 2. Separate preparations were found to be reproducible, e.g. the phosphorus contents of all batches lay in the range 2·0–2·1%. 3. Ninhydrin-positive compounds in hydrolysates accounted for 43–46% of the cell wall and 79–87% of the nitrogen of the cell wall. Examination of the results for individual ninhydrin-positive compounds showed that 5–15% of the cell wall was murein and about 30% protein. 4. Trypsin treatment of crude cell-wall preparations preferentially liberated arginine, lysine and leucine, but it was not clear whether these arose from cell-wall or cytoplasmic proteins.
