A high-speed network typically assigns each admitted connection a fixed bandwidth, somewhere between its mean and peak transmission rate. As an alternative, we develop a novel scheme for re-assigning network resources periodically on the basis of current network conditions. Our algorithm, which employs the theory of fuzzy logic control, is computationally efficient, making frequent bandwidth re-allocations over relatively small time intervals feasible. In situations where traffic intensities change drastically over short time intervals, our algorithm, tested against both static and non-fuzzy bandwidth re-allocation schemes, significantly lowers data loss while increasing network efficiency.