The influence of various parameters controlling the chemical vapour deposition of carbon-boron-nitrogen mixtures has been studied using the experimental designs methodology which provides a valuable phenomenological approach for the initial study of complicated chemical systems. The gaseous precursors used were acetylene (C2H2), boron trichloride (BCl3), and ammonia (NH3). An extended experimental field was investigated, which leads to a very wide composition range for the deposits. All the deposits may be described as hexagonal single phase, including the C-BN-"BC3" ternary domain. In this composition triangle, no thermodynamically stable boron carbides were found.