Abstract 1.1. A method is described for the quantitative estimation of the approximate quantities of cottonseed allergen absorbed from the digestive tract when CS-1A and cottonseed are ingested. The method may be generally applied to other allergens and has potential applicability in fundamental studies of the diffusibility of allergens from the gastrointestinal tract. 2.2. Ten micrograms of CS-1A introduced intramuscularly were approximately equivalent to 100,000 γ of ingested CS-1A in capacity to incite passive-transfer reactions. On this basis, when 100 mg. of CS-1A were ingested, 0.01 per cent of the allergenic fraction was absorbed. 3.3. One hundred micrograms of CS-1A introduced intramuscularly were approximately equivalent to 800,000 γ of ingested CS-1A in reagin-neutralizing power. According to this criterion, when 800 mg. of CS-1A were ingested, 0.013 per cent of the allergenic fraction was absorbed. 4.4. One hundred micrograms of CS-1A introduced intramuscularly were approximately equivalent 50 20,000,000 γ of ingested cottonseed in reagin-neutralizing capacity. 5.5. Eight-tenths of a gram of ingested CS-1A was approximately equivalent to 20 Gm. of ingested cottonseed in reagin-neutralizing power. 6.6. The method described may be applicable to the determination of the relative concentration of an allergen in two substances by comparing the quantities of the ingested substances required to induce equivalent effects in passively sensitized sites. By this method it was estimated that CS-1A contains a concentration of allergen approximately twenty-five times as great as defatted cotton-seed.