Haemophilus influenzae cultivated on chocolate agar. Cultivation 24 hours, 37 °C in an aerobic atmosphere enriched with 5% carbon dioxide.

Chocolate agar contains red blood cells (usually sheep erythrocytes), which have been lysed by heating very slowly to 56 °C. The agar is named for the color and does not contain any actual chocolate ;-).
Other chemicals are also added to the medium. These include V factor, some vitamins, coenzymes, amino acids, dextrose, ferric ion and other factors which improve the growth of Haemophilus spp. The incorporation of bacitracin (a polypeptide antibiotic) facilitates the selective isolation of Haemophilus species and inhibits Gram-positive bacteria.