Acetylenic and diacetylenic liquid crystalline monomers have been prepared in order to obtain conjugated polymers with an orientational character. Unlike the polydiacetylene derivatives obtained and which do not exhibit any mesomorphic behaviour, a smectic phase, stable over a large temperature range, occurs in the case of all the polyacetylenes. This mesophase appears to be stabilized by anin situpolymerization of the monomers oriented in the nematic state. After iodine doping, a nematic phase appears in the polymer in addition to the smectic phase. AC complex conductivity measurements, realized over a large frequency range. are reported for some doped and undoped polyacetylenes. Preliminary results concern both non-oriented polymers and an undoped polymer in which the mesogenic groups have been oriented after polymerization.