The gelling abilities and hot-paste viscosities of four commercial acid-modified maize starches were studied. The microstructure of the heated 15% starch dispersions was investigated using light microscopy, and the molecular weight of amylopectin and amylose determined by HPLC with post-column iodine staining. The two high-amylose starches, Hi-Set CHG and Ultra/Set LT, were shown to be stronger gelling agents than the acid-modified waxy starch (Product 06090) or the ordinary acid-modified maize starch (Farinex CO2). The very high gelling properties of Ultra/Set LT were due to the presence of high-molecular weight amylose-type material and a high amount of amylose in the continuous phase under the heating conditions used. Farinex CO2 was least degraded and had the highest hot-paste viscosity and mean molecular weight. Product 06090, the acid-modified waxy starch, did not form a gel on cooling, but had the lowest hot-paste viscosity.