Detection of protein variation in human serum by externally released precipitins from the blue crab, Callinectes sapidus.

1. A number of invertebrate species releases precipitins into the environment. This process is apparently part of an externally directed immunologic system. 2. A saline solution of precipitins released from the blue crab, Callinectes sapidus, provided a reagent that produced two different precipitation reactions with proteins from the sera of human individuals. 3. One of the reaction variants was also detected with mammalian antiserum, the other was not. The former variant was associated with a medical condition: hypergammaglobulinemia. 4. Saline reagents from different invertebrate species may prove useful in clinical diagnosis and for revealing new human protein polymorphisms.