The calculation of the cross-sections for the inactivation of enzymes and viruses has been made, assuming these to be 1-hit detectors. The calculation makes use of a power-law empirical formula for the radial distribution of dose about the path of an energetic heavy ion. The calculation is made by assuming that the probability of inactivatinga molecular target by irradiation with a given dose of delta rays is equal to the probability of inactivating it with the same dose of gamma-rays. The cross-section is found by adjusting the assumed value of the D,37, dose of gamma-rays until an optimal fit of the calculation to the measured cross-sections is obtained. Taking all 72 cross-section measurements into account, the average ratio of experimental to calculated cross-sections is 0.96±0.11, while the average ratio of the experimental to the fitted value of the gamma-ray D,37, dose is 1.07±0.18.