AbstractWe describe a method based on gel electrophoresis for the quantitation of strand breaks in DNA and demonstrate its application to the measurement of single‐ and double‐strand breaks formed by γ‐rays for DNA irradiatedin vitro. For single‐strand breaks, our data span the dose range from 0.1 to 1 Gy, while for double‐strand break doses were from 3 to 15 Gy. In agreement with results obtained using other techniques, we find that the dose response function for single‐strand breaks is linear while the dose response function for double‐strand breaks is curved, indicating that it is the sum of both linear and quadratic components. We discuss factors that determine the sensitivity of the method and indicate approaches to make possible the quantitation of strand breaks in the DNA of cells irradiated with s