Monoparticulate layers of dodecylbenzenesulfonic acid-stabilized, 34.0-, 29.4-, and 26.5-angstrom-diameter CdS clusters have been formed at air-water interfaces in a Langmuir film balance. Surface pressure vs surface area isotherms and Brewster angle microscopy demonstrated that increasing surface pressure resulted in transitions from well separated to well-compressed monoparticulate layers and, ultimately, to multiparticulate layers. CdS particles with diameters of 34.0, 29.4, and 26.5 angstrom formed films with critical areas per particle (conceptually analogous to headgroup areas) of 1100, 800, and 650 angstrom2, respectively, which corresponded well to the values calculated by assuming hexagonal close packing of hard spheres (887, 749, and 608 angstrom2). Sequential transfer to solid substrates, by the Langmuir-Blodgett (LB) technique, led to the formation of multiparticulate layers of size-quantized CdS clusters. Absorbances of CdS in the LB film were found to increase linearly with the number of layers transferred, substantiating the uniformity of deposition. The position of the absorption edge was invariant between the CdS particles in chloroform solution and in LB films. Fluorescence maxima of the CdS particles, however, shifted from 510 nm in chloroform to 455 nm in LB films.