Lutetium oxyorthosilicate (LSO) was employed as scintillator material in a positron lifetime (PALS) fast-slow spectrometer. Compared to the widely used BaF2 scintillator material, LSO has a single exponential decay with 40 ns, a high density of 7.49 g/cm3, an effective nuclear charge of 65.8 and a superb light output. With this features photon rates above 5·106 should be possible, which affords to obtain lifetime spectra within a period of minutes. The physical and mechanical properties make LSO attractive as scintillator material for PALS measurements. The capability of LSO for PALS was studied and compared to BaF2. As a first test of the spectrometer, a lifetime spectrum of well annealed nickel was measured and analyzed.