This paper describes the muon pretrigger system of the HERA-B experiment. The muon pretrigger is designed to detect track candidates for muons in order to generate seeds for the first level trigger (FLT) search algorithm. Muons provide the cleanest event signature in the large amount of hadronic background. In order to achieve the required precision the muon pretrigger system has to cope with an interaction rate of about 40 MHz at the HERA bunch crossing rate of 10.4 MHz. This results in a total input data rate of about 10 Gbyte/s. A total rate reduction by a factor of 200 is aimed at by the complete FLT, including the pretrigger systems (electromagnetic calorimeter, muon and high-p/sub T/), within at most 12 /spl mu/s.