An exteriorized loop of mouse intestine was exposed to low-energy electrons, where the dose rate decreased by a factor of 5 from the base of the crypt to the top of the proliferative zone. A crypt survival curve was obtained, expressed in terms of exposure time. The shape of the curve was interpreted in terms of survival parameters for colony-forming cells (clonogens) derived using¹³⁷ Cs γ rays and the depth-dose curve measured for electrons. It is concluded that the shape of the crypt survival curve using electrons is inconsistent with the notion of either the presence of a large number of clonogens or a small number near the top of the proliferative zone. A computer fitting procedure showed that the best agreement between predicted and observed curves was achieved with 2.7 ± 0.5 clonogens at cell position 5.6 ± 0.6, in the putative stem-cell zone.