Summary form only given. Carbon nanotubes are predicted to exhibit large nonlinear optical properties due to their extensive conjugated structure. Nonlinear behaviour such as optical-limiting has been reported for both carbon nanotubes and graphite. Fullerenes, which can be considered as diminutive versions of carbon nanotubes, are well known to posses large and fast nonlinear optical properties. The magnitude and the bandwidth of optical nonlinearities in these materials are predicted to increase with the number of constituent carbon atoms per molecule. Carbon nanotubes, there fore, provide an attractive prospect for nonlinear optical investigations. We investigated the linear absorption and nonlinear photoluminescence in multiwall carbon nanotubes (MWNT) and graphite suspensions. Multiphoton absorption induced photoluminescence was observed in the visible region.