The behaviour of iron in ZnS has been studied through effect of iron concentration on magnetic and electrical properties. Synthetic specimens containing 0.09 to 16.6 atom percent iron were found to behomogeneous. At lower iron concentrations, sphalerites are paramagnetic and magnetic susceptibilities vary with iron content in a linear manner; at higher concentrations, they become increasingly antiferromagnetic and susceptibilities vary in a nonlinear manner. Antiferromagnetic behaviour may be like that in Mn-bearing ZnS, the result of magnetic ordering of substitutional iron. Electrical conduction for natural iron-bearing sphalerite is from migration of low-mobility holes rather than electrons, is consistent with the mechanism known as d-band conduction, and is possible in iron-containing ZnS through interaction of Fe (super 3+) with Fe (super 2+) with Fe (super 3+) in tetrahedral or octahedral position.