Effects of cortisol and anaphylaxis on the uptake of catecholamines (CA) in the guinea pig lung have not been investigated previously. Sensitized and healthy animals were randomly killed, catheters were inserted into the pulmonary artery and vein, and the preparation was perfused with Tyrode. Half of the animals received 50 mg. of cortisol 2 hours before the procedure. H3-epinephrine (E) or norepinephrine (NE), 10 ng. per milliliter, was infused for 6 minutes. Infusion was started 15 seconds prior to challenge with ovalbumin or NaCl. Total -H3 and NE(E)-H3 were determined in the lung homogenates. Results showed (1) 6 to 14 per cent of circulating CA were retained by the lung. (2) In healthy animals cortisol inhibited NE uptake by 35 per cent and E uptake by 15 per cent. (3) Anaphylaxis increased NE and E accumulation by 10 and 19 per cent, respectively. (4) Regardless of experimental conditions approximately 40 per cent of NE and 30 per cent of E taken up were recovered unchanged. CONCLUSIONS (1) There is significant uptake of CA in the lung. (2) One of the mechanisms of therapeutic effect of cortisol in asthma might be its inhibitory effect on CA uptake. (3) Increased CA accumulation during anaphylaxis could be beneficial by increasing the local concentration of amines, or detrimental by decreasing availability of CA, depending on the uptake site and cell type and degree of subsequent metabolism. (4) Cortisol and anaphylaxis per se appear not to change degradation of CA.