If dialysis is successful for the treatment of schizophrenia, the artificial kidney must be removing something which the human kidney cannot, unless other nonspecific factors are involved. Either there is an abnormal compound present which is retained by normal renal tubular transport processes, or the kidney of a schizophrenic must be abnormal in that it fails to excrete a normally present compound. Since the latter explanation is less probable, biochemical research should focus on classes of compounds which are known to be handled differently by the artificial kidney than by the human kidney. A dialyzable “schizophrenic toxin” might be a nonprotein, nonprotein-bound compound of molecular weight below 500 daltons such as an organic acid or base. Proteins, peptides, amino acids, and trace elements are less likely possibilities.