Fragmentation of unconfined cylindrical specimens of rock due to stress wave loading has been investigated using a Split Hopkinson Bar (SHB). Photographs were taken during the fracture process using a high-speed framing camera, and incident, reflected and transmitted stress pulses were recorded using a digital transient recorder. The energy absorbed by the specimen during the fragmentation process was evaluated from the recorded stress pulses. Two different rocks were studied, namely Bohus granite and Solenhofen limestone. The specimen length was 50 mm, and the diameter was 25 mm. The incident pulse durations were 50, 100 and 200 μs, and the amplitude was in the range of 0·5-4 kbar. The high-speed photographs show that fracture occurs as previously observed for other rocks using SHB-devices. Notably, the main crack orientation is axial, and the degree of fragmentation increases with increasing load. The energy absorption of the specimen increases markedly when the load applied approaches a certain value. For the Bohus granite specimens the critical load was found to be 1·8 times the static compressive strength, and for Solenhofen limestone it was 1·3 times the static compressive strength. Two simple specimen models were analyzed theoretically, namely, one linearly-elastic and one rigid-plastic. The first model gives the best agreement with experimental results if the degree of fragmentaion is low, the second model gives the best agreement if the degree of fragmentation is high. The rigid-plastic model explains the experimental observation that the specimen always absorbs less than half the incident pulse energy.