CO₂ mediated induction of pollen adhesion, germination, tube penetration, tube growth through the stylar tissue and seed set was studied inBrassica campestris L. var. toria following incompatible pollination. This report stresses the effect of CO₂ not at a single step but at various levels which normally prevent and/or hinder successful fertilization and seed set. The possible role of CO₂ in overcoming these barriers is discussed.