Studies have been carried out using ion-exchange analysis for determination of urinary purines, pyrimidines, and nucleosides in children with immunodeficiency disorders. Using cation and anion-exchange techniques, the following compounds of urine have been quantitatively determined: deoxyadenosine, adenosine, adenine, pseudouridine, 7-methylguanine, N 2,N 2 -dimethylguanosine, hypoxanthine, and xanthine. Excretion levels of these compounds did not differ significantly from normal values in six children with various immunodeficiency diseases, excluding severe combined immunodeficiency. However, of the seven children studied with severe combined immunodeficiency disease (normal adenosine deaminase), four showed increased excretion levels for one or more of the compounds studied. A germ-free child with severe combined immunodeficiency had lower excretion levels than the mean normal value for most of these same compounds. The possibility is considered that the increased excretion levels noted may be a consequence of repeated episodes of infection in most children with severe combined immunodeficiency.