Cylindrical CsI(Tl) scintillators of 38 mm diameter and 100 mm length read out with PIN diodes of 400 mm2 area were tested with respect to their response to medium energy light particles (p, d, t, α). Resolutions of better than 1% were achieved for 50 MeV protons and 90 MeV α-particles. For many crystals the resolution was found to be limited to 2–3% by local crystal nonuniformities which caused variations of the light output efficiency of several percent. A bench test is described which allows the detection of inhomogeneities to better than 0.5% accuracy. The quality of particle identification obtained with ΔE-E and pulse shape discrimination techniques are investigated as a function of count rate.