Intestinal absorption of cystine and cysteine in normal human subjects and patients with cystinuria.

1. An intestinal perfusion technique has been used to study absorption in uivo of L-cystine and L-cysteine in six normal human subjects and three patients with homozygous cystinuria. 2. No significant absorption of L-cystine was detected during perfusion of the cystinuric patients, whereas L-cysteine absorption was normal. These results imply that L-cystine and L-cysteine are normally absorbed by different transport processes. 3. No significant reduction of L-cystine to L-cysteine occurred in the gut lumen during the perfusion experiments. No more oxidation of L-cysteine to L-cystine occurred in the gut lumen during the perfusion experiments than in the test solutions which were simultaneously incubated in uitro.