Aluminium-silicon irregular eutectic alloy was melted in a graphite crucible in vacuum. This alloy was directionally solidified at a constant growth rate, V (8.3 mum/s) and at different temperature gradients, G (2.0-7.8 K/mm) and also with a constant G (7.8 K/mm) and different V (8.3-498.7 mum/s) in the Bridgman type directional solidification furnace. The interflake spacings, lambda(i), were measured from both transverse and longitudinal sections of the specimens. The relationships between interflake spacings, lambda(i) and solidification parameters V and G were obtained by linear regression analysis method. The variations of interflake spacings, lambda(i) with V, G and undercoolings, DeltaT(i), were investigated and the relationships between them were examined. Operating parameters phi and eta which reflect the spacing adjustment mechanism were obtained. lambda(i)(2)V, lambda(i) DeltaT(i), DeltaT(i)V(-a), lambda(i)(3)G and DeltaT(i)G(-b) values were determined by using lambda(i), V, G and DeltaT(i), values. The results obtained in this work have been compared with the eutectic theory and previous experimental results. (C) 2003 Elsevier B.V. All rights reserved.