I am inclined to agree MikeG and they had quite simple methods of doing so already available when the two rovers, Spirit and Oppertunity, went to Mars but it was not seen as a sufficently important experiment, given that the rovers were designed to act as geologists rather than biologists.
Thing is, given the levels of electromagnetic radiation (significantly ultraviolet) experienced on the Martian surface, it seems unlikely that life of any kind would survive in easily accesible areas and if life is present it is more likely to be underground where conditions could be more favourable?
