We have purified to homogeneity two distinct 10-kDa proteins with potent chemotactic activity for neutrophils from porcine alveolar macrophages incubated for 24 h with Escherichia coli endotoxin (lipopolysaccharide (LPS), 10 micrograms/ml). Neutrophil chemotactic activity in alveolar macrophage supernatants was concentrated by adsorption to SP-Sephadex, and purified by cation exchange and reversed phase high performance liquid chromatography. The first peptide, alveolar macrophage chemotactic factor (AMCF)-I, had chemotactic activity for both porcine and human neutrophils. The chemotactic activity for porcine neutrophils was detectable at 3 x 10(-10) M, peaked at 3 x 10(-8) M, and was comparable to that of zymosan-activated porcine serum. Segmental instillation of AMCF-I into porcine lungs caused marked neutrophil accumulation at 4 h in both bronchoalveolar lavage fluid and in lung tissue. The second peptide, AMCF-II, was active at 1.4 x 10(-9) M for porcine neutrophils, but it was less active for human polymorphonuclear neutrophils than was AMCF-I. Oligonucleotide probes to regions of the N-terminal sequences of AMCF-I and AMCF-II hybridized to mRNA recovered from LPS-stimulated alveolar macrophages. The N-terminal sequences and amino acid compositions indicate that AMCF-I and AMCF-II are distinct proteins, but that both have homologies with a family of peptide chemoattractants produced by human blood monocytes and platelets. Thus, alveolar macrophages stimulated with LPS produce two distinct 10-kDa cytokines with potent chemotactic activity for neutrophils. This indicates that there are two different peptide pathways by which alveolar macrophages can recruit neutrophils into the lung.