To provide a therapeutic agent and a diagnosticagent for mitochondrial dysfunction brain diseasesincluding cerebral infarction as a representative.A therapeutic agent for a mitochondrial dysfunctionbrain disease, which comprises (A) .delta.-aminolevulinic acidrepresented by the formula (1), a derivative thereof, ora salt thereof and (B) an iron compound in combination.R2R1NCH2COCH2CH2COR3 (1)wherein R1 and R2 each independently represents a hydrogenatom, an alkyl group, an acyl group, an alkoxycarbonylgroup, an aryl group, or an aralkyl group； and R3represents a hydroxy group, an alkoxy group, an acyloxygroup, an alkoxycarbonyloxy group, an aryloxy group, anaralkyloxy group, or an amino group.
