Estimated GFR less than 30 mL/min/1.73m(2). The rational is that 1) sirolimus therapy is most likely to be beneficial during the early phase of FSGS, before progressive fibrosis in the glomeruli and interstitium has become the dominant abnormality and may be irreversible, and 2) we wish to enroll patients who are unlikely to progress to ESRD within the one year treatment period.