We describe a procedure for determining the five principal urinary porphyrins--uroporphyrin, heptacarboxylporphyrin, hexacarboxylporphyrin, pentacarboxylporphyrin, and coproporphyrin--by using high-performance liquid chromatography (HPLC). The method involves a 12- to 15-min isocratic separation on a Bondapak Phenyl column. Studies have indicated that urine samples must be preserved to maintain porphyrin stability for extended periods. We have found that the pH of preserved samples must be adjusted into the acidic range before the samples can be accurately analyzed by this HPLC procedure. Our studies demonstrate that good reproducibility and recovery are achieved with this method. Urinary porphyrin values for normal and porphyric individuals are reported.