Lesbian vampirism is a trope in 20th-century exploitation film and literature that has its roots in Joseph Sheridan le Fanu's novella Carmilla (1872) about the love of a female vampire (the title character) for a young woman (the narrator):
Sometimes after an hour of apathy, my strange and beautiful companion would take my hand and hold it with a fond pressure, renewed again and again; blushing softly, gazing in my face with languid and burning eyes, and breathing so fast that her dress rose and fell with the tumultuous respiration. It was like the ardour of a lover; it embarrassed me; it was hateful and yet overpowering; and with gloating eyes she drew me to her, and her hot lips travelled along my cheek in kisses; and she would whisper, almost in sobs, 'You are mine, you shall be mine, and you and I are one for ever'. (Carmilla, Chapter 4).
This was a way to hint at or titillate with the taboo idea of lesbianism in a fantasy context outside the heavily censored realm of social realism. Also, the conventions of the vampire genre—specifically, the mind control exhibited in many such films—allow for a kind of forced seduction of presumably heterosexual women or girls by lesbian vampires.
Dracula's Daughter (1936) gave the first hints of lesbian attraction in a vampire film, in the scene in which the title character, portrayed by Gloria Holden, preys upon an attractive girl she has invited to her house to pose for her. Universal highlighted Countess Zaleska's attraction to women in some of its original advertising for the film, using the tag line "Save the women of London from Dracula's Daughter!"
Le Fanu's Carmilla was adapted by Roger Vadim as Blood and Roses in 1960. More explicit lesbian content was provided in Hammer Studios production of the Karnstein Trilogy of films loosely adapted from Carmilla. The Vampire Lovers (1970) was the first, starring Ingrid Pitt and Madeline Smith. It was a relatively straightforward re-telling of LeFanu's novella, but with more overt violence and sexuality. Lust for a Vampire (1971) followed, with Yutte Stensgaard as the same character played by Pitt, returning to prey upon students at an all-girls school. This version had her falling in love with a male teacher at the school. Twins of Evil (1972) had the least "lesbian" content, with one female vampire biting a female victim on the breast. It starred real life twins and Playboy playmates Madeleine and Mary Collinson. Partially due to censorship restraints from the BBFC (Hearn and Barnes 1998), Hammer's trilogy actually had fewer lesbian elements as it proceeded.