Summary form only given. Transient nonlinear optical spectroscopy has been a powerful tool for the study of fundamental processes in semiconductor systems. We use transient differential transmission (DT) to study the spin relaxation of excitons in the ground state of an ensemble of InAs self-assembled quantum dots. The sample investigated consisted of a single layer of InAs quantum dots, grown in the Stranski-Krastenow mode. Cross-sectional STM measurements confirmed the quality of the dots following post-growth rapid thermal annealing. The use of circular polarizations allows for the direct study of spin-related processes of the dot ground state. Because the DT measurements are performed resonantly, there is no complication due to excited state relaxation, unlike the case of PL measurements.