Prognosis of systemic sclerosis (SSc) depends on internal organ involvement. We assessed the value of renal function reserve (RFR) for the detection of preclinical nephropathy in scleroderma. Thirty SSc patients with normal serum creatinine and 30 healthy controls were included. Medsger disease severity score, glomerular filtration rate (GFR), and microalbuminuria were measured. Tc-99m DTPA was utilized for GFR measurement at baseline and after oral protein overload (stimulated GFR). RFR was calculated as the percentile increase of stimulated GFR. SSc patients had lower means of baseline GFR (P=0.001), stimulated GFR (P=0.004), RFR (P=0.046), and higher microalbuminuria (P=0.009) than controls. According to baseline GFR, SSc patients showed three categories-normal baseline GFR (n=12), hyperfiltration GFR (n=3), and reduced baseline GFR (n=15). In the former category, RFR was normal in 6/12 patients and abnormal in the remainders (50%). Hyperfiltration patients and those with reduced baseline GFR showed abnormal RFR. A statistically significant negative association was found between microalbuminuria versus stimulated GFR and RFR (r= -0.5, P=0.007 and r= -0.45, P=0.013, respectively). The majority of SSc patients with abnormal RFR had disease duration of ≥48 months (60% vs. 20%, P=0.008). All SSc patients with pulmonary hypertension had abnormal RFR, while reduced baseline GFR was noted in only 60%. A significant negative correlation was found between reduced baseline GFR and cumulative dose of corticosteroids in SSc patients (r= -0.4, P=0.022). RFR estimation could be a useful predictive marker for preclinical renal involvement in SSc patients so that early prophylactic measures and therapy modifications could be considered.