An experimental apparatus, based on laser light diffraction, was developed and used to study changes in drop size distribution during a single injection, as well as from injection-to-injection, in a diesel fuel spray in room air. A model-independent numerical procedure was developed to infer drop size distribution from measured diffracted light energy.It is believed that spray deflectors, used to reduce optical density in the core of the spray, considerably influenced drop sizes. Data collected from undisturbed outer edges of the spray indicated that large numbers of sequential sprays must be sampled to accurately determine true distribution mean and dispersion parameters. Drop size distributions at all sampled locations were bi-modal, with spray axis locations exhibiting the greatest fractions of small drops. During a single spray, at a fixed location in space, the Sauter Mean Diameter varied approximately inversely as the fuel line pressure.