 Chemotherapy was administered every 21 days for up to 6 cycles in subjects with aggressive non-Hodgkins lymphoma NHL; mantle cell or diffuse large B-cell lymphoma. Subjects were administered R-CHOP on day 1 of each cycle. All subjects were randomized to 1 of 2 treatment arms: arm A subjects were administered pegfilgrastim 6 mg on day 1 of each cycle within 4 hours of chemotherapy completion; arm B subjects were administered pegfilgrastim 6 mg on day 2 of each cycle at least 24 hours after chemotherapy completion. All subjects were administered placebo on the day they did not receive pegfilgrastim. A total of 77 subjects were enrolled at 24 centers across the US. Protocol treatment duration for subjects was up to 18 weeks 6 three-week cycles. 