Non-linear optical response of single-wall carbon nanotubes, produced without catalyst, was investigated. Third-order susceptibility Degenerate Four Wave Mixing measurements have been performed on thick film of nanotubes deposited onto quartz substrate. Results are presented as measured in the nanosecond time scale at 532 nm. The second-order hyperpolarizability gamma was estimated to be as large as 1.6 x 10(-29) e.s.u. (C) 2003 Elsevier B.V. All rights reserved.