['To investigate the antiapoptosis effect of sphingosine-1-phosphate (S1P) on human fetal ovarian tissue treated by cyclophosphamide (CTX).', 'Experimental animal study.', 'University center for reproductive medicine and IVF unit.', 'Female immunodeficient BALB/c nude mice, 6 to 8\xa0weeks old.', 'Human fetal ovarian tissue slowly cryopreserved then subcutaneously transplanted in immunodeficient mice.', 'Follicle survival assessed qualitatively and quantitatively using H&E staining, and cellular apoptosis of the ovarian grafts evaluated using transmission electron microscopy and DNA nick end labeling in situ (TUNEL assay).', 'The alkylating agent CTX caused a substantial follicle loss and apoptotic DNA fragmentation in the ovarian grafts in a period of 2\xa0weeks of transplantation. The S1P treatment significantly prevented follicular apoptosis and maintained primordial follicle population in the grafts.'] Does sphingosine-1-phosphate suppress cyclophosphamide induced follicle apoptosis in human fetal ovarian xenografts in nude mice?