A new multichannel MAC protocol called Hop Reservation Multiple Access (HRMA) for packet-radio networks is introduced, specified and analyzed. HRMA is based on very-slow frequency-hopping spread spectrum (FHSS) and takes advantage of the time slotting necessary for frequency hopping. HRMA allows a pair of communicating nodes to reserve a frequency hop (channel) using a hop reservation and handshake mechanism on every hop to guarantee collision-free data transmission in the presence of hidden terminals. HRMA provides a baseline to offer QoS in ad-hoc networks based on simple half-duplex slow FHSS radios. We analyze the throughput achieved in HRMA for the case of a fully-connected network assuming variable-length packets, and compare it against an ideal multichannel access protocol and the multichannel slotted ALOHA protocol. The numerical results show that HRMA can achieve much higher throughput than multichannel slotted ALOHA in the traffic-load ranges of interest, especially when the average packet length is large compared to a slot size, in which case the maximum throughput of HRMA is close to what can be obtained with an ideal protocol.