The incidence of childhood leukaemia in Britain has increased dramatically during the last century. This increase has mainly affected the under five age group, in whom the risk increased by more than 50 per cent in the second half of the century alone.

The causes of leukaemia in children are not well understood and the reasons for the increasing incidence are unknown. This is the driving force behind the conference - Childhood leukaemia: incidence, causal mechanisms and prevention - which is being hosted by CHILDREN with LEUKAEMIA, Britain's leading charity devoted to the conquest of the disease.

Environmental factors are thought to play a major role in the increasing incidence and as Alan Preece, Professor of Medical Physics at the University of Bristol, explains, the unborn child is particularly sensitive to the effects of exposure to environmental agents. Placental transfer determines the exposure of the foetus to these agents as a result of maternal exposure.

Preece and his team at Bristol set out to determine the extent of placental transfer through a series of bio-distribution measurements and ex vivo experiments using donated human placentas. They found reasonable correlation between the placental transfer data from different models, allowing preliminary calculations of dose to foetal organs.

Preece reports "We found that foetal organ concentrations can exceed those of the mother which may have implications due to the increased sensitivity of the foetus. The exact levels are as yet unknown but we know that childhood leukaemia is initiated in utero and this could well be a factor in the initiation. Consideration must now be given to the likely risk estimates."

Top international experts from Europe, America, Asia and Australia will converge on London to discuss this and a wealth of other research being presented over the five days of the conference. Many of the usual suspects will be covered - including radiation, parental smoking, viruses and air pollution. But other concepts that have so far received little attention will also be highlighted. These include, for example, diet in early life, melatonin and circadian rhythms, light pollution and medicines in pregnancy.

It is hoped that out of the conference will be born an agenda for future research and CHILDREN with LEUKAEMIA will be launching a £1m fund to support research in priority areas.