Nine female patients with normal serum total thyroxine (T4) and triiodothyronine (T3) but elevated thyroid stimulating hormone (TSH) levels were studied. Six patients had generalised oedema associated with maximal diurnal weight gains in excess of 1.4 kg. Under conditions of forced water diuresis, before and during physiological replacement of 1-thyroxine, the supine transcapillary escape rate of albumin (TERA) was measured, while the venous colloid osmotic pressure (COP), packed cell volume (PCV) and urinary excretion of water and electrolytes were studied in both the supine and upright positions. The TERA, diurnal weight gain and orthostatic increase in COP fell significantly with treatment. In the six patients with oedema and excessive diurnal weight gains, the retention of salt and water on tilting was reduced with thyroxine treatment. In female patients we consider generalised oedema associated with excessive diurnal weight gain, to be a common and early symptom of hypothyroidism, meriting thyroxine replacement therapy.