Baverstock, a British radiobiologist who is monitoring the effects of the 1986 Chernobyl nuclear reactor explosion, says that no one has explained the reason for the seeming higher risk for Jews.

In any case, the risk of thyroid cancer among children exposed to radiation is still low, he stressed.

The WHO's Chernobyl project in Belarus has not examined the effects of radiation on specific ethnic groups, he said.

But differences in reactions are not surprising. Among any large group of individuals, for example, some have much stronger reactions to radiotherapy, Baverstock said.

The WHO intends to launch a case-controlled study in Minsk to compare various groups and look at factors that may affect the influence of radiation.

Organizations of immigrants from the former Soviet Union have complained in recent years that the Health Ministry has declined to screen them for diseases that could result from the Chernobyl disaster.

Instead, health funds simply treat any diseases that appear.