Several aspects of the comparative physiology and pharmacology of renal urate handling are considered; with special attention to bidirectional transport, the existence of intrarenal urate synthesis and degradation in certain species, and the nature and sites of the reabsorptive and secretory processes. Interspecies variations in the sensitivity of the kidney to uricosuric agents and the degree of specificity of the secretory mechanism are discussed. A variety of techniques, especially as applied in certain nonhuman primates, have led to a concept of very rapid trans-tubular fluxes of urate – a concept which may apply in ma