Alloys of compositions Al-6Nd, Al-9Ce, Al-16Nd and Al-22Ce (wt%) were prepared by chill-block melt-spinning at a surface speed of similar to 29 m s(-1) into ribbons of thickness between 20 and 70 mu m. The melt-spun ribbons were heat treated for 2 h at 200, 300, 400 and 500 degrees C. The as-spun and heat-treated ribbons were tested for microhardness and investigated by optical and transmission electron microscopy and X-ray diffraction. Age hardening was not observed for any of the alloys, indicating only a limited amount of extended solid solubility as a result of the melt-spinning conditions used. Al-9Ce and Al-6Nd were found to be relatively stable at a hardness of similar to 90 HK0.01 and 75-80 HK0.01, respectively, unaffected by heat treatment at up to 300 degrees C for 2 h, but heat treatment for 2 h at 400 or 500 degrees C caused softening. Al-6Nd and Al-9Ce as-solidified ribbons comprised a cellular Zone B structure with alpha Al cells (of size similar to 0.5 mu m) and intercellular orthorhombic alpha Al-11(Nd,Ce)(3). The hardness of Al-16Nd as-spun was measured as 330 +/- 20 HK0.01 unchanged by heat treatment at 200 degrees C for 2 h, while heat treatment for 2 h at higher temperatures caused softening. As-spun Al-16Nd consisted of Zone A only comprising alpha Al solid solution and orthorhombic alpha or tetragonal beta Al11Nd3 partly coherent with the matrix. Al-22Ce had a hardness of 330 +/- 20 HK0.01 as-spun but softened on treatment for 2 h at 200 degrees C. As-spun Al-22Ce consisted partly of Zone A structure extending from the wheel side of the ribbon through half of the thickness. The remaining part of the ribbon consisted of cellular Zone B (cell size similar to 0.2 mu m) with intercellular alpha Al/alpha Al11Ce3 lamellar eutectic together with areas that were 100% lamellar eutectic (interlamellar spacing 0.09 +/- 0.02 mu m) All the as-spun microstructures showed coarsening upon heat treatment at sufficiently high temperature. The resulting microstructure after treatment at 500 degrees C for 2 h consisted of a bimodal distribution of alpha Al-11(Nd,Ce)(3) which formed as large particles on the grain boundaries and smaller ones in the grain interiors. The corresponding microstructure was less coarse for Al-16Nd and Al-22Ce.