Granulocyte-colony stimulating factor (G-CSF) is used to mobilize CD34+ haematopoietic stem cells from the bone marrow to the peripheral blood. We proposed to use cell subsets induced by G-CSF to slow down disease progression in patients with amyotrophic lateral sclerosis (ALS). Patients with definite or probable ALS were assigned in a double-blind manner to receive G-CSF or placebo every three months for a year. The primary outcome measure was the functional decline, measured by the revised ALS Functional Rating Scale, Revised (ALSFRS-R) score. Secondary outcome measures included vital capacity, manual muscle strength, compound muscle action potential amplitudes, neurophysiological index, and McGill single item quality of life score (QoL). Thirty-nine patients were enrolled. Seventeen patients who received G-CSF and 18 who received placebo were evaluated. G-CSF was effective in mobilizing CD34+ to blood. The outcome measures used showed no statistically significant benefit, although there was a trend of slowing disease progression following two G-CSF treatments, as shown by lower slopes of ALSFRS-R and QoL in the first six treatment months. The treatment had no major side-effects. G-CSF administration in ALS patients caused successful mobilization of autologous bone marrow cells, but was not effective in slowing down disease deterioration.