Thirty eight, chronic, perennial asthmatic children were prospectively examined every six months for a mean 8.9 years to clarify the relation between clinical asthma and puberty. Improvement in the disease occurred independent of puberty but the rate of improvement was appreciably greater during puberty. This led to speculation that improvement in childhood asthma could be associated with an immunological process capable of receiving a powerful stimulus from hormones active during puberty. In addition, children whose illness improved before any sign of puberty had developed could be confidently predicted to 'grow out' of their disease. Conversely, if no improvement was seen by the onset of puberty, a much more guarded prognosis was needed.