Thirty individuals with history of immediate, objective, adverse reactions after shrimp ingestion underwent double-blind, placebo-controlled shrimp-food challenges. All individuals who did not exhibit a positive response (reproduction of objective symptoms) were administered an open challenge of 16 whole cooked shrimp. Positive challenge responses occurred in 9/30 subjects (30%); six of these subjects experienced a positive response during the double-blind phase. Of the 21 remaining subjects, 12 experienced generalized pruritus as their only symptom, whereas nine subjects had completely negative challenge responses. All placebo challenges were negative. Although a positive skin test was strongly associated with challenge symptoms (p less than 0.001), the shrimp prick skin test titration end points were not different among the challenge groups. The serum shrimp RAST percent was significantly higher in the positive challenge group (p less than 0.02). Mean levels of shrimp-specific serum IgG, IgA, and IgM levels were not different among the challenge groups. Although no single immunologic variable could be consistently used to identify subjects more likely to exhibit a positive challenge response, the composite of a positive shrimp prick skin test and elevated serum shrimp-specific IgE (RAST percent label bound greater than 11%) demonstrated a correct predictive value of 87% in this group of shrimp-sensitive subjects.