CR-39 plastic track detector (Homalite) has been tested for its response to light particles (protons, alpha particles) and heavy ions ( 238U, 32S, 252Cf fission fragments, 19F, 16O and 12C) having a wide spectrum of energies. Perpendicular and oblique geometries were employed, and the exposed detectors were etched in stages in 6N NaOH at 70 ± 1°C. The track parameters like etch pit diameter, etched track length, and etching velocity along the track ( V t ) were obtained at the end of every etching stage. Both, Optical-Microscope (O.M.) and Scanning-Electron-Microscope (SEM) were utilized in these measurements. It has been found that the Etch-Rate Ratio (ERR = V t / V g ) for CR-39 is related to REL, the Restricted Energy Loss (in units of MeV cm 2g -1) of charged particles through the relation, ERR = 7.51 × 10 -8 ( REL) 2.36 for REL values exceeding 2 × 10 3 MeV cm 2 g -1. Similarly, the results show that ERR = 7.24 × 10 -7 ( Z 2 eff / β 2) 1.92 for Z 2 eff/β 2 values exceeding 3 × 10 3. The Restricted Energy Loss (REL) has been found to be related to Z 2 eff/β 2 through the relation (REL) ωo = 200 eV = 2.62 (Z 2 eff/β 2) 0.81 It has also been observed that the prolonged etching of CR-39 in stages (short intervals) enables us to make a rough classification between ‘light’ and ‘heavy’ reaction products such as those emitted in high energy nuclear interactions. The rate of track etching is significantly enhanced when the etchant becomes saturated with the etched products.