An apparatus for the measurement of optically detected magnetic resonance (ODMR) in zero magnetic field at 4.2 K using commercially available parts is described. A simple electronic analogue device is used to obtain kinetic data from ODMR transients in a fast and reliable way. From these data decay rates of the three spin levels of the lowest molecular triplet state can be obtained, whereas populating rates can be determined within defined limits. Since the apparatus is suited for unguarded operation during long periods of time, signal averaging of weak signals, e.g., from biological molecules, is particularly easy. Kinetic data have been obtained for dihydroporphin, which can be considered as the structural basis for chlorophyll:k1= 121±12 sec−1;k2=277±28 sec−1;k3=22±2 sec−1; 0.28<P1<0.43;P2=1;P3<0.08, wherekiandPiare the decay and populating rates of theith spin level.