Manuscript number 888 of the Collection of Arabic manuscripts of the Royal Monastery of San Lorenzo of El Escorial (Spain) contains a small treatise composed by physician and pharmacologist ʿĪsā b. Māssah al-Baṣrī (9th century). This work offers a detailed description of different causal agents that originate the sexual impulse and its culmination, the coitus. The treatise enumerates and interprets the physical factors that conform man’s sexual response, which is viewed as a purely physiological process, as well as the cultural and psychological factors that shape and modulate the sexual preferences of each individual.