AbstractA definite increase in two low molecular weight factors, G10-2 and G10-3 was found in Ehrlich ascitic fluids, parallel to tumor growth. The isolation and identification of the two factors were attempted through gel filtration and reversed phase column chromatography, using ascitic fluids obtained 13 days after intraperitoneal implantation of Ehrlich tumor cells. As a result, two highly purified factors were observed upon examination by high performance liquid chromatography. Additional analytical data, collected by UV spectrum, NMR spectrum and mass analysis. allowed us to identify G10-2 as uric acid and G10-3 as uracil.Detailed immunological analysis of uric acid and uracil revealed that the augmenting activities of mouse and human NK cells by mouse IFNδ/βor human rIFNδA/D were impaired in the presence of either compound at concentrations of 0.07 mM, the concentration detectable in theascitic fluidof tumor bearing mice.