To provide a therapeutic agent and a diagnostic agent for mitochondrial dysfunction brain diseases including cerebral infarction as a representative. A therapeutic agent for a mitochondrial dysfunction brain disease, which comprises (A) ´-aminolevulinic acid represented by the formula (1), a derivative thereof, or a salt thereof and (B) an iron compound in combination. €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒR 2 R 1 NCH 2 COCH 2 CH 2 COR 3 €ƒ€ƒ€ƒ€ƒ€ƒ(1) wherein R 1 and R 2 each independently represents a hydrogen atom, an alkyl group, an acyl group, an alkoxycarbonyl group, an aryl group, or an aralkyl group and R 3 represents a hydroxy group, an alkoxy group, an acyloxy group, an alkoxycarbonyloxy group, an aryloxy group, an aralkyloxy group, or an amino group.
