Anaphylactoid responses of two types of genetically different rats to horse serum and yeast.

Rats selectively bred for non-reactivity to clinical dextran (NR rats) fail to exhibit the anaphylactoid reaction to systemic baker's yeast or horse serum. Rats which respond with an anaphylactoid reaction to clinical dextran (R rats) react to baker's yeast but do not react to horse serum. The widespread oedema produced in R rats by systemic baker's yeast provides yet another clear method of differentiating them from NR rats.