The growth and nutritional requirements of Haemophilus ducreyi (CIP 542T) were determined in liquid media by impedance technology. We found that H. ducreyi grew in a liquid mixture of Proteose Peptone No. 3, hemin, L-serine, glucose, L-glutamine, and inorganic salts. The peptone in the medium was essential for H. ducreyi growth, and the growth factor (or factors) in the peptone was stable to autoclaving (15 min, 121-degrees-C) and could not be extracted with organic solvents (2:1 chloroform/methanol) from either acidic (1 N CH3COOH), neutral (pH 7.1), or basic (1 N NaOH) solutions. Hemin was also an essential component for the growth of H. ducreyi, but a much lower concentration of hemin (5.0 mug/ml) was required than has been previously reported in the literature (25 mug/ml). Using impedance technology to measure H. ducreyi doubling times, we showed that bovine albumin enhances H. ducreyi growth.