Using an antiserum directed at the COOH-terminus of tachykinins, we have examined postmortem tissue from two cases of metastatic ileal carcinoid for the presence of tachykinin-like immunoreactivity. The vast majority of the immunoreactive tachykinin-like material eluted from a Sephadex G-50 column as two peaks at positions corresponding to molecular weights of 1300 and 850. The 1300 dalton peak was resolved by reverse-phase-HPLC into two components which by Edman sequencing, amino acid analysis, and fast atom bombardment (FAB)-mass spectrometry criteria, were identified as substance P and substance K. The 850 dalton peak was also resolved on RP-HPLC into two peaks which were resistant to Edman degradation but from amino acid analysis and FAB-mass spectrometry criteria were identified as pyro-Glu-substance P 5-11 and oxidized pyro-Glu-substance P 5-11. In control experiments substance P 5-11 was converted to pyro-Glu-substance P 5-11 during the extraction procedure. Both tumors also contained a minor immunoreactive peak which eluted from a Sephadex G-50 sizing column at a position corresponding to a molecular weight of 4000 which probably represents neuropeptide K. These results suggest that beta-preprotachykinin is preferentially expressed in carcinoid tumors and that substance K may also play a role in the carcinoid syndrome.