The concentration of certain metabolites and amino acids appears to be changed in patients with the painful bladder syndrome interstitial cystitis. A study of the metabolism of the arylalkylamines (tryptophan, tyrosine, tyramine, phenylalanine) was carried out in 250 patients (237 females, 13 males), revealing an inability to synthesise normal amounts of serotonin and MHPG, a noradrenaline metabolite. Furthermore, the absence of ammonia and tryptophan in urine confirmed the presence of a membrane leak. Dietary restriction lessened the symptoms but did not alter specific abnormalities in dopamine metabolism. Dietary management offers a cost-effective therapeutic approach.