Accumulating evidence suggests that inflammation plays a major role in the pathogenesis of motoneuron death in amyotrophic lateral sclerosis (ALS) both in humans and transgenic mouse models. Peroxisome proliferator-activated receptors (PPARs) are involved in the inflammatory process. Agonists of PPAR-alpha, -gamma, and -delta show anti-inflammatory effects both in vitro and in vivo. We investigated the therapeutic effect of pioglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, in the G93A SOD1 transgenic mouse model of ALS. Orally administered pioglitazone improved motor performance, delayed weight loss, attenuated motor neuron loss, and extended survival of G93A mice as compared to the untreated control littermate group. Pioglitazone treatment extended survival by 13%, and it reduced gliosis as assessed by immunohistochemical staining for CD-40 and GFAP. Pioglitazone also reduced iNOS, NFkappa-B, and 3-nitrotyrosine immunoreactivity in the spinal cords of G93A transgenic mice. These results suggest that pioglitazone may have therapeutic potential for human ALS.