for the Histiocyte Society Background. Previous reports have suggested activity of the nucleoside analogues 2-chlorodeoxyadenosine (2-CdA) and 2Πdeoxycoformycin (2Π-DCF) in Langerhans cell histiocytosis (LCH). Procedure. To assess the efficacy of 2-CdA and 2Π-DCF as salvage therapy for LCH, a survey of members of the Histiocyte Society and a literature review were undertaken. Twenty-three patients treated with 2-CdA and 4 treated with 2Π-DCF were found, age range 2 months to 49 years. Results. All 15 survey patients had multiorgan involvement, and 14 were heavily pretreated. Doses of 2-CdA ranged from 0.1 mg/kg/day continuous infusion for 5-7 days (majority of patients) to 13 mg/m 2 /day for 5 days, for 1-6 courses. One of the 15 patients had an early death, 5 had no response (NR), 3 had partial response (PR), and 6 achieved complete response (CR). Among 8 published patients, 7 achieved stable CR and 1 NR. Among 4 patients treated with 2Π-DCF (4 mg/m 2 /week for 8 weeks then q 2 weekly), 2 achieved CR for 16+ and 18+ months and 2 PR for 2 and 5 months. Toxicity consisted mainly of combined myelo-and immunosuppression but no significant infections occurred and there were no toxic deaths. A cumulative thrombocytopenia was noted, which in 1 case took up to 6 months to resolve. Transient gastrointestinal toxicity and elevation of liver enzymes was seen, and 2 patients developed renal tubular acidosis. The peripheral neuropathy reported in adult patients receiving high doses was not seen. Conclusions. 2-CdA and 2Π-DCF appear to have a useful role in LCH and are worthy of prospective trial in patients unresponsive to routine therapy. Med. Pediatr. Oncol. 33:476-481, 1999.