Composite materials formed by metal nanoclusters embedded in silicate glasses exhibit enhanced third-order electrical susceptibility, whose real part is related to the intensity-dependent refractive index. This parameter can be determined by the Z-scan method, provided that the material is stable under high-power laser irradiation. In this work, metal nanocluster composite glasses are prepared by different procedures involving the use of ion beams, and analyzed by the Z-scan method. The role of laser-composite interaction effects in the analyses is investigated. (C) 2000 Elsevier Science B.V. All rights reserved.