In situ technique of thermal analysis-mass spectroscopy coupling was employed to investigate the growth of carbon nanotubes (CNTs) by means of chemical vapor deposition of benzene at the temperature of 700 degreesC. It was found that the building blocks of CNTs depended on the coverage of benzene over the catalyst. As soon as the molecules of benzene were introduced onto the catalyst at high temperature, a fraction of small hydrocarbon fragments were generated and these fragments likely participate in the construction of CNTs. As the catalyst was heavily covered at room temperature, there is no hydrocarbon fragments detected, which led to the growth of CNTs in the six-membered-ring-based model as we early suggested. (C) 2004 Elsevier B.V. All rights reserved.