Ten patients on long term lithium therapy (mean four years, range 1-10.5 years) were subjected to various renal, thyroid, haematological, cardiac and endocrine tests. There was impaired urinary concentrating ability in seven subjects, which was not responsive to vasopressin stimulation, suggesting a partial nephrogenic diabetes insipidus. Nine subjects had metabolic acidosis with higher urinary pH than expected suggesting presence of acidification defect in the kidney. No significant change in renal function, thyroid function, ECG or haematological parameters were detected. Our findings concur with previous reports from the West regarding the safety of lithium administration.