In one hospital over a 15-month period, four out of nine patients ventilated for acute severe asthma developed acute hydrocortisone myopathy. All patients had received less than 1.0 g day-1 hydrocortisone. Affected patients had severe generalized weakness which recovered over 1-6 weeks. When myopathic and unaffected subjects were compared, there was no clearcut difference with respect to age, sex, types of drug used, serum potassium levels, duration of ventilation and muscle paralysis, total dose of vecuronium bromide, or mean daily doses of hydrocortisone. The main difference between the two groups was in the total doses of hydrocortisone. The myopathic patients all received greater than 5.0 g hydrocortisone (range 5.4-10.2 g) and the others less than 4.0 g (range 0.9-3.5 g). The possibility that neuromuscular blockade might predispose to the development of myopathy is discussed. Hydrocortisone myopathy can occur when less than 1.0 g day-1 is used, and even with as little as 5.4 g given over 6 days.