Abstract When steel is cast, voids are generally formed in the workpiece due to material shrinkage or gas entrapment during solidification. It is desirable that these weak points in the material should be eliminated by void closure in the ensuing hot working process. Interest in void closure has increased in recent years because of the replacement of conventional casting by continuous casting. The cross-section of the continuously cast material is usually small in comparison with that of an ingot and consequently at the present time void closure is often required to take place for even small reductions. This work comprises a basic investigation into the closure of artificial voids of equal size and of square distribution. The closure is studied for homogeneous plane strain forging with parallel dies and is analysed theoretically with an upper bound solution and experimentally with Filia wax and slip-line field wax as model materials. Theory and experiment are found to be in good agreement. According to the theoretical model, the rate of void closure increases with reduction. It is emphasised that it is disadvantageous to turn the workpiece too early. Experiments have also been carried out with specimens containing voids of random distribution. According to the results, the theoretical model seems to have some relevance to such specimens also.