It is shown that the Viterbi decoding algorithm can be modified for use in a type-I hybrid-ARQ (automatic-repeat-request) scheme. Through proper definition, the partial path metrics can be made directly proportional to the error content in a received sequence. Retransmission requests are generated whenever all partial path metrics exceed a fixed threshold before decoding is completed. The threshold may be varied to balance reliability with retransmission frequency. The implementation of this scheme increases reliability performance by several orders of magnitude at the expense of minimal modification to the basic Viterbi decoder and, in some cases, a negligible decrease in throughput. >