Rates of asthma among children appear to have stabilised, according to a survey of youngsters in Aberdeen.
Asthma rates appear to have stabilised in recent years
But the pioneering study, which spans 35 years, identified an increase in the diagnosis of both eczema and hay fever.
More than 3,500 children were involved in the survey, which was first carried out by Aberdeen University in 1964.
It found that the diagnosis of asthma in children with a wheeze rose from 28% then to 64% in 1994 - but increased by just 3% over the following five years.
The survey was carried out at the same schools which took part in the 1964 study.
The study of the city's pupils, which takes the form of a questionnaire to parents, was revived in 1989 and has been repeated every five years since then.
In the first survey, asthma had been diagnosed in 73 of the 261 youngsters with a wheeze.
By 1989 that figure had risen to 331 (49%) of the 675 children with a wheeze.
The figure climbed again in 1994, when 654 (64%) of the 1,025 children with a wheeze had been diagnosed with the condition.
The results of the 1999 survey, which have been published in the British Medical Journal, showed that 67% of youngsters had been diagnosed with asthma.
The researchers said: "In Aberdeen, the prevalence of symptoms suggestive of asthma now seems to be stable.
"The proportion of children with symptoms in whom asthma has been diagnosed is high, suggesting that the widespread publicity given to asthma has paid off.
"Indeed, a higher rate of diagnosis might well be undesirable, leading to asthma drugs being given inappropriately - for instance, to children with chronic cough."
When the study was first carried out the condition was diagnosed in twice as many boys as girls, but the gap has narrowed to a point where the two sexes are almost equal.
However, the research did highlight a "small but significant" increase in the number of children with eczema or hay fever between 1994 and 1999.
Researchers at Aberdeen University carried out the study
The figures rose from 18% to 21% and from 13% to 15% respectively.
In 1964, the levels had been 5% and 3.2%, although both had risen to 12% by 1989.
"The continuing increases between 1994 and 1999 in diagnosed eczema and hay fever suggest that the tendency for children to develop allergies is still increasing, although these increases may also in part reflect changes in diagnostic fashion," said the report.
It said the new findings suggested that the rate of rise in childhood asthma had slowed, although a quarter of primary school children had been diagnosed as having the condition at some time in their lives.
"Most of the recent increase can be attributed to increased diagnosis in children with symptoms; increase in wheeze is barely significant," added the researchers.