The growth undercooling Delta T and eutectic interlamellar spacing lambda have been measured as functions of growth velocity V and temperature gradient G for matrix Al-Si eutectic in the presence of primary silicon in Bridgman-grown hypereutectic Al-18.3 wt % Si alloy. Delta T/V-1/2 shows a step decrease at V > 270 mu m s(-1) corresponding to a change in eutectic growth morphology from flake-like to fibrous, but there was no corresponding change in lambda V-1/2. Analysis of published data on the effect of G on lambda V-1/2 for the Al-Si eutectic shows good agreement with the single relationship lambda V-1/2 = A G(-n) with A = 56+/-8 mu m(3/2)s(-1/2)(K mm(-1))(n) and n = 0.24+/-0.03 for the range 0.1 < V < 6 x 10(4) mu m s(-1) and 0.7 < G < 2000 K mm(-1).