In this communication, we have measured, using a T-jump with light scattering detection, the relaxation time associated with the fusion-fission process in a surfactant concentration range where the shape of micelles varies from a sphere to rodlike or wormlike. The Sodium dodecyl sulfate (SDS) was chosen because SDS micelles grow at high ionic strength. Measurements have been carried out in brine with 0.6-1 mol/L NaCl at 35 degrees C. The measurements of the relaxation frequency as a function of the SDS concentration have been fitted by a theoretical expression. The fits dismiss the fact that the end cap of micelles is a simple hemisphere. Assuming that the end cap diameter is larger than that of the cylindrical part, a size distribution is proposed which favors the spherical micelles. This hypothesis disadvantages the micelles with sizing close to twice be length of a spherical micelle, because they have negative bending without the cylindrical part. We obtained values of the fusion probability of micelles.