The chemical diagnosis of tyrosinemia type I generally involves the detection of succinylacetone (SA) in patient urine. However, 5-aminolevulinate (5ALA), which accumulates due to succinylacetone's inhibition of porphyrin synthesis, can also be used as diagnostic metabolites. Here we examined the stabilities of these markers on dried urine filter paper. After two weeks at room temperature, the succinylacetone was 10% of its original level, but over 80% of 5-aminolevulinate remained. Thus, although insufficient succinylacetone was recovered from dried urine filter paper to diagnose tyrosinemia type I, 5-aminolevulinate was readily detected, permitting the diagnosis.