Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motor neurons. We report the safety and functional efficacy results of a double-blind, placebo-controlled phase II study of xaliproden, a non-peptidic compound with growth factor activities, in 54 ALS patients treated for up to 32 weeks. In order to overcome the interference of mortality with functional assessment in exploratory studies, we identified from our ALS database prognostic factors to establish a staging process for selection pf patients: age, disease duration, slopes of deterioration of the functional scores calculated during the two months prior to the inclusion, and the value at entry of the forced vital capacity (FVC). The six months intent-to-treat analysis showed no statistically significant effect but a trend in favour of 2 mg xaliproden compared to placebo for reduction in the rate of deterioration of FVC, limbs functional score, and manual muscle testing score (MMT). The results in the completer analysis showed a significant 43% slower rate of deterioration in FVC (P=0.046) in xaliproden-treated patients but not in functional and MMT scores. These results support the use of a staging process to select suitable patients for phase II studies, and suggest that xaliproden may have potential effects in ALS and deserve further study.