The three-machine flowshop scheduling problem with interval processing times, where processing times are within a lower and an upper bound, is studied. The objective is to minimize makespan. Given that the problem is NP-hard, some heuristics are proposed. The proposed heuristics are assessed based on numerous experiments. The data for the experiments were randomly generated for different number of jobs and different distributions, where both symmetric and skewed distributions are considered. The number of replications considered for each combination of the number of jobs and the distribution was one hundred. Error of each heuristic was reported. Computational experiments indicated that one of the proposed heuristics significantly performs better than the other heuristics.