Abstract: Middle molecules in sera of uremic patients (UMM) were isolated on Sephadex G-15 gel-filtration Chromatography eluted with triethylamine caibonate buffer. Dry sample of middle molecules could be obtained with lyophilization. From the dialysis fluids of the uremic patients treated with continuous ambulatory peritoneal dialysis (CAPD) the same UMM fractions could be obtained. The behaviours of gel-filtration chromatography, UVand JRabsorptions of UMM from the sera and the dialysis fluids of uremic patients were identical. In 206nm and 235 nm, there were 2 UVabsorption peaks and in 3246, 1516, 1122 and 613 cm^-1there were 4 characteristic IR-absorption peaks which are not found in normal sera. The Compositions responsible for the behaviours of UV and IR absorptions are found in the third sub-peak after the middle molecules were further separated by ion-exchange chromatography. The contents of peptides and free amino acid from the sample of UMM were quantitatively analyzed. They are between one to three percent.

Key words: Uremic, Middle molecules, Continuous ambulatory peritoneal dialysis, Gel-filtration chromatography