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) δ-aminolevulinic acid represented by the formula (1), a derivative thereof, or a salt thereof and (B) an iron compound in combination. R2R1NCH2COCH2CH2COR3 (1) wherein Rl and R2 each independently represents a hydrogen atom, an alkyl group, an acyl group, an alkoxycarfconyl group, an aryl group, or an aralkyl group and R3 represents a hydroxy group, an alkoxy group, an aeyloxy group, an alkoxycarbonyloxy group, an aryloxy group, an aralkyloxy group, or an amino group.
