Porphyrias are diseases caused by inherited or adquired inhibition of enzymes of the heme biosynthetic pathway, what is in the core proteins like haemoglobin, myoglobin and cytochromes. There are eight catalytically steps in this metabolic way. Excepting the first, defects in other enzymes may cause accumulation of porphyrin metabolites in the body tissues and fluids, as delta(5)-aminolevulinic acid (ALA). Two inherited diseases cause ALA-overload (acute intermittent porphyria and inherited tyrosinemia) and one adquired syndrome (lead poisoning). Pathogenesis of ALA-accumulating porphyrias is not fully understood, mainly neurological symptoms (convulsions). In addition, treatment of seizures is not easy, because majority of anticonvulsive exacerbate porphyria crisis. In last years it was identified participation of reactive species in the genesis of neurological alterations caused by ALA, what may suffer a self-cycle of oxidation and promote a cascade of free radicals generation. Lipids in biological bilayers are especially susceptible, but also proteins and little molecules (-SH groups).