Electrical resistance tomography (ERT) techniques under development appear to offer exciting possibilities for future non-intrusive, full-field measurement of gas-liquid and miscible liquid mixing characteristics. A ＇full＇ 3-D electrical resistance tomographic analysis composed of a 3-D image reconstruction algorithm and a 3-D sensing strategy is being developed at UMIST to overcome the problem of using only a 2-D analysis for inherent :I-D problems. A diagonal sensor excitation and measurement protocol is being examined for the sensing strategy. The image reconstruction algorithm is based on the Newton-Gauss method together with a variant of Occam＇s regularisation. Experiments were conducted on a 2.7 m(3) mixing vessel. The vessel is represented by a 3-D finite element model with 1536 voxels for an initial test with 4 sensing planes. A total 3969 voltage measurements can be obtained from the diagonal strategy from which only 2016 are independent measurements. Some initial results are presented with reconstructed images of multi-object phantom configurations and the resulting air-core vortex arising from stirring the mixing vessel with a Rushton impeller at 140 rpm.