A field experiment on an acid soil of Shillong, in 1982 and 1983, investigated the comparative performance of Mussoorie rockphosphate (MRP), single superphosphate (SSP) and their combinations for potatoes. MRP, when applied alone, proved much inferior to SSP, on an equal P basis, in tuber characters, tuber yield and nutrients (N, P and K) uptake. Application of SSP together with MRP improved the efficiency of the latter. SSP and MRP combinations in 25:75, 50:50 and 75:25 proportions, on a P basis, were 79·3, 95·8 and 101·2% as effective as SSP in terms of tuber production. The response to P was optimum at 70 kg P/ha with SSP and was linear up to the highest rate (105 kg P/ha) with the combinations of SSP and MRP. Concentration of N in tubers declined with the increasing amounts of P, whereas P and K concentrations were little affected.