Basaltic rocks are potential rocks for alkali-silica reaction (ASR). The objective of this study is to determine reactivity of the basalts of different compositions and textures. The study was carried out on basalts that are widespread in the Middle Anatolian Region of Turkey. They form the major source of local crushed rock aggregates. Early Quaternary Melendiz volcanites, Quaternary Karatas volcanites and Igredag basalts were selected around the Nigde Region, and the experimental studies were conducted on these rocks. The samples were collected as being representative of I I different basalt types. The basalts were firstly classified according to their petrographical and chemical composition. Petrographic techniques and accelerated mortar bar test were then used to evaluate the potential alkali reactivity of the basalt aggregates. The basalts having acidic-intermediate character and matrix that is mainly composed of volcanic glass are potentially suitable for alkali-aggregate reaction (AAR) according to the standard values. (c) 2004 Elsevier Ltd. All rights reserved.