Production of the F42 adhesive factor by porcine enterotoxigenic Escherichia coli (ETEC) grown on minimal solid medium was glucose-dependent. The addition of alanine and sodium acetate to this medium repressed the expression of this antigen whose production was also inhibited when the pH of the growing medium was lower than 7.4. The antigen was extracted from F42-positive ETEC grown in minimal liquid medium supplemented with 0.5% glucose. The cells were suspended in buffered 1 M NaCl and heated at 60 degrees C. The supernatant was then treated with ammonium sulphate and the resulting precipitate treated with deoxycholate followed by chromatography of the deoxycholate-soluble material on Sepharose-4B. The molecular weight of F42 purified antigen was near 31,000 daltons and its pI 3.2, as determined by polyacrylamide gel electrophoresis and isoelectric focusing, respectively. Immunoelectrophoretic studies showed that the purified F42 antigen presented a slight anodic migration and was recognized only by its homologous antiserum.