The formation of etched tracks in solid-state nuclear track detectors is usually described assuming an unequivocal correlation of the etch rate ratio with the energy loss of charged particles. For protons, deuterons and alpha particles this assumption could be verified within the scatter of the experimental data. Experimental studies with Li-7, B-11 and C-12 ions yielded, however, systematic deviations from the expected results. Analysing the complete experimental data set for CR-39, a dependence of the etch rate ratio was found not only on the particle's energy loss, but also on the depth within the detector where this energy loss occurs. Arranging the etch rate ratio as a function of both these variables all experimental results appear without inconsistencies. The etch rate ratio represented by a two-dimensional matrix can be used, then, for characterising the etch kinetics along the trajectories of charged particles of different kinds and initial energy. (C) 2002 Published by Elsevier Science Ltd.