Globoid cell leukodystrophy is an autosomal recessive disease with progressive demyelination caused by a deficiency of the lysosomal enzyme galactosylceramidase. Bone marrow transplantation (BMT) is a therapeutic option for patients with late-onset disease and for patients with early onset disease that had an early diagnosis owing to an affected sibling. This therapy, however, typically is not effective for early onset disease when the diagnosis occurs after several months of life. In an effort to enable a broader range of patients to benefit from BMT, we tested whether combining substrate-reduction therapy with BMT would result in a greater benefit than either treatment alone in the twitcher mouse model of globoid cell leukodystrophy. Twitcher mice treated with l-cycloserine, an inhibitor of 3-ketodyhydrosphingosine synthase, and transplanted with 50 ± 5 × 106bone marrow cells on d 10 had a mean life-span of 112 d compared with 51 d for BMT alone (p< 0.001) or l-cycloserine alone, which was previously reported to be 56 d. l-Cycloserine treatment also was initiated neonatally to determine whether it would allow for a delayed BMT to have therapeutic value. Twitcher mice given only BMT at 18 d or only a short course of l-cycloserine died at 36 and 37 d, respectively. Twitcher mice given a short course of l-cycloserine + BMT at 18 d lived to 58 d (p= 0.0006). In conclusion, substrate-reduction therapy enhanced the value of BMT in twitcher mice, suggesting that this combination strategy might benefit patients with globoid cell leukodystrophy.