N.m.r. linewidth studies are described for 115In in aqueous solutions of the nitrate and sulphate. Because it has a large nuclear electric quadrupole moment, 115In has short relaxation times and the effects on these of (a) viscosity and (b) symmetry of molecular environment, are investigated. Hydrolysis at low concentrations increases the linewidth, and in the nitrate solutions, but not the sulphate, weak complex formation increases linewidth at high concentrations. Chemical shift data also support this interpretation. Complexes are formed in indium halide solutions and exchange rates for In3++ InX2+⇌ InX2++ In3+ are calculated by the exchange broadening of the 115In line on adding small amounts of halide to In(ClO4)3 solutions. A similar calculation is made for the InCI–4/CI– exchange. The resonances of the species InX–4(X = Cl,Br,I) in ethereal solution are described and a table of linewidths and shifts given. In conc. aqueous HCl and HBr other less symmetrical species are present.