CommentThe cause of uraemic pruritus is unknown. In some cases it may be due to secondary hyperparathyroidism. Only in these patients is parathyroidectomy indicated.2 The mechanisms of other treatments such as ultraviolet light3 or cholestyramine4 are unknown and are effective in only some cases. In our patient the rapid and complete disappearance of pruritus after lowering the dialysate magnesium concentration suggests a causative relation between itching and serum magnesium concentration. Lowering the dialysate magnesium concentration is known to restore nerve conduction velocity towards normal in patients receiving CHD,5 and this could be the reason for the complete disappearance of the pruritus in our patient.

A double-blind within-patient investigation was performed to determine whether the interposition of an extension tube (10 cm length x 3 -2 cm diameter) between a metered dose inhaler and the mouth alters the bronchodilator efficacy of terbutaline sulphate. On two consecutive study days 14 adult patients with stable reversible airways obstruction inhaled a cumulative dose of 500 jig of terbutaline which was delivered from a metered dose inhaler with or without the extension tube attached and received placebo in a similar manner. The drug was inhaled in doses of 125, 125, and

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