Magnetic resonance imaging (MRI) was performed on 22 patients with a wide spectrum of pituitary disease and on 17 control subjects, in order to determine whether MRI is useful in localising and determining the extent of involvement of large and small pituitary tumours. The results indicate that MRI, with an 0.5 T superconducting magnet (Elscint, Israel), can be used to visualise large pituitary tumours and to determine the extent of parasellar and suprasellar involvement. The ‘empty sella’ syndrome can also be easily and confidently diagnosed. Some microadenomas can be visualised despite the relatively thick slices (0.7 cm) used in this study. These findings suggest that MRI in its current state of development is very useful in evaluating large pituitary lesions. With further technical refinements, improving the spatial resolution and decreasing slice thickness, this technique may come to be of some importance in the evaluation of pituitary microadenomas.