Electrochemical lithium insertion into magnesium titanate spinels of composition Mg2-yTi1+yO4 (y=0.33, 0.57) has been investigated. Insertion into the y=0.33 spinel appears to take Place via a two-phase equilibrium reaction, as indicated by both cell potential and lattice parameter measurements. The insertion process for the y=0.57 spinel appears to be somewhat different, with a minimum in unit cell parameter and a marked drop in cell potential being observed at an Li content of about 0,2 per formula unit. This is thought to reflect a change in the dominant insertion mechanism as the reaction progresses. The magnetic properties of the spinel were found also to depend upon the degree of substitution, with some inserted samples exhibiting spin-glass glass type behaviour. The structure of the sample was found to change markedly on heating in an inert atmosphere, both a rocksalt type phase and a spinel phase, with a much decreased unit cell edge, were encountered after heating to about 500-degrees-C in an inert atmosphere.