A method of operating a radio communication system uses a random access channel to enable a secondary station to transmit a message to a primary station. The secondary station transmits a preamble (102) to the primary station. After successful receipt of the preamble the primary station transmits a control channel (502) including power control information to instruct the secondary station to adjust the output power of its transmitter. This method ensures that the secondary station transmits at a sufficient power for the message (104) to be received successfully by the primary station, while minimising interference generated by the transmission.