In 1955 Brennan tried his hand at a new endeavour, and his imprint Macabre House was launched with the publication of the pamphlet H.P. Lovecraft: An Evaluation (now incredibly scarce, like many of the other Brennan-published efforts).
The Macabre House imprint also published most of Brennan's horror fiction in the 1950s to early 1970s, such as the volumes The Dark Returners (1959), Scream at Midnight (1963) and The Casebook of Lucius Leffing (1973).