Seven patients with glycogen storage disease type Ib suffering from severe and/or recurrent bacterial infections were treated with glycosylated recombinant G-CSF (Lenograstim). Mean follow up was 20.8 months (range 9-30 months). In all cases a median dose of 5 micrograms/kg/day resulted in rapid clinical improvement, associated in 6/7 with an increase in absolute polymorphonuclear (PMN) count. In the remaining subject, a striking amelioration of infectious status contrasted with a persistently low PMN count. Liver transplantation in one patient resolved metabolic complications but did not improve PMN count or the infectious status, while neutropenia was corrected by G-CSF. Prevention of recurrent infections was achieved in all cases with intermittent therapy. Short term treatment was well tolerated, thrombocytopenia in two patients (WHO grade 0 and grade 3) recovering after decrease of G-CSF dosage.