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Spin-reorientation transitions in Nd1-xPrxFe11Ti compounds have been studied by measuring the temperature dependence of the a.c. susceptibility and the magnetization. The angular dependence of the magnetization on the applied field was measured on magnetically aligned samples in a SQUID magnetometer. In NdFe11Ti, the easy magnetization direction at room temperature was determined by x-ray diffraction to be the c-axis; at low temperatures, the SQUID measurements show a cone to be stable. At temperatures between 170 and 250 K, the SQUID measurements display more complex behaviour, which is attributed to the occurrence of a first-order magnetization process in this compound. The easy magnetization direction of Nd1-xPrxFe11Ti compounds with 0.2 less than or equal to x less than or equal to 0.4 changes from easy c-axis at high temperatures via a basal plane to easy cone at low temperatures. The magnetic phase diagram of the Nd1-xPrxFe11Ti system is given. For PrFe11Ti, the critical field of the FOMP transition below 230 K, which corresponds to the critical temperature of the first-order transition, and the anisotropy fields at temperatures ranging from 240 to 300 K have been further investigated by means of the SPD technique.