Microcalorimetry experiments were carried out on aqueous micellar solutions of hexadecyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr). We have investigated the effect of surfactant concentration and of the salt content upon the specific heat. The curves of the specific heat versus temperature exhibit a maximum resulting from the transition between spherical and elongated micelles. The temperature T-max of these maxima depends on surfactant and salt concentration as expected from simple theoretical arguments. Static and dynamic light scattering experiments were performed on the same systems. The results show that light scattering and microcalorimetry experiments yield a different kind of information : blob size and variation of the micellar length. Microcalorimetry provides an interesting tool for determining the micellar growth.