At least some of the patients have E. coli 0157:H7, a particularly toxic strain.

Many colleagues and I have worked with hundreds of toxic strains.

But in this case Dr. Burkholder has declined to make her toxic strain of Pfiesteria widely available.

Dr. Burkholder said she had given her toxic strain of piscicida to 17 different laboratories.

Dr. Burkholder's allies support her decision not to make her toxic strain freely available.

"Burkholder put in for a major grant to grow the toxic strain of pfiesteria and provide it to anyone who wanted," Dr. Lubchenco said.

"The grant went to other labs who haven't been able to culture and deliver the toxic strains."

Dr. Ranke-Heinemann's polemic is meant to confront Catholic leaders with the toxic strains in their tradition.

Both toxic and nontoxic strains exist.

But a toxic strain that lives in cattle without effect on them can be passed to humans with fatal consequences.