Directional solidification experiments have been carried out on different Al-Cu alloys as a function of solidification parameters, temperature gradient G, growth rate V, and composition C-0. The specimens were solidified under steady state conditions with a constant temperature gradient (7.4 K mm(-1)) at a wide range of growth rates (9-490 m s(-1)) and with a constant growth rate of 9.5 mum s(-1) at a wide range of temperature gradients (1.0-7.4 K mm(-1)). Microstructural parameters, the primary dendrite arm spacing lambda(1), secondary dendrite arm spacing lambda(2), dendrite tip radius R, mushy zone depth d were measured and expressed as functions of solidification parameters, G, V and C-0 by using a linear regression analysis. The results were in good agreement with previous experimental work and current theoretical models suggested for dendritic growth. (C) 2002 Elsevier Science B.V. All rights reserved.