The nonlinear susceptibility, (chi) (3), and nonlinear refractive index, n2, of a range of dithiolenes: metal-sulfur ligand complexes bearing simple H, alkyl and aryl substituents have been measured by degenerate four wave mixing (DFWM) and self focussing/defocussing (z-scan) at 1.064 micrometers using 100 ps pulses. Materials with the largest coefficients consistent with low linear and two photon absorption, for example bis[1-ethyl-2- phenylethene-1,2-dithiolate(2-)-S,S'] nickel have been modified to be soluble as guests in PMMA host polymers, n2's as high as 10-8 cm2/kW have been found but intermolecular interaction causes increased two photon absorption at the high loading necessary for this n2. Some simple chemical modifications which may improve figures of merit are suggested. Power requirements for simple waveguide devices using these materials are estimated and it is concluded that improved materials are still needed. Dithiolenes have sufficient variability in structure to suggest that this may be achievable with new derivatives of the same family.