The pressure-area isotherms of mono- and divalent octadecylpyridinium M(dmit)2 charge transfer salts (M = Au, Pd or Pt) are presented and the behaviour contrasted with previously reported results for tetraalkylammonium M(dmit)2 salts. The current voltage characteristics of Y-type Langmuir-Blodgett films of both salts showed similar behaviour upon doping with bromine or iodine vapour. Immediately upon doping the conductivity of the films increased by many orders of magnitude but within a few hours this enhanced conductivity had decreased to an almost stable value which was still several orders of magnitude greater than in the undoped film. Interestingly, in this state the current-voltage characteristic showed a clear square-law behaviour. Within a day or two, however, the contribution of this process to the overall conductivity decreased to reveal a stable ohmic behaviour from which the film conductivity was estimated to be 0.06 S m-1.