A man has been accused of posting "indecent or obscene" material to people, including those connected with animal testing for medical research.
Andrew Kirk, 46, from Middlesbrough, denied 18 charges when he appeared at Birmingham Crown Court on Monday.
Alleged recipients of Mr Kirk, of Swanage Close, include a Staffordshire councillor who was a witness in a civil case involving animal research.
Also, the chief executive of animal testing firm Huntingdon Life Sciences.
Mr Kirk, who appeared in court wearing a white T-shirt with the slogan "Vivisection is Scientific Fraud", is also accused of targeting an MP and a CPS lawyer, as well as a taxi firm which took cleaners to an undisclosed laboratory.
The exact nature of the letters, sent between November 2004 and February this year, was not disclosed and the case was adjourned for a two-day trial starting on 7 November.
Darley Oaks Farm in Newchurch, Staffordshire, has been the subject of protest from animal rights campaigners over the last six years and announced in August that it would be closing its guinea pig breeding operations at the end of the year.