Heterosexual men aged 18-45 exhibited elevated salivary alpha-amylase to slideshows of men kissing and disgusting images like maggots. Responses to men kissing matched disgust images and exceeded neutral images like paper clips. Stress response occurred regardless of self-reported prejudice against gay men. Even men with very low prejudice showed heightened physiological reaction to men kissing. Reaction independent of self-reported aggression toward gay men. Authors note difficulty distinguishing physiological disgust from anxiety. Finding undermines gay panic defense used in hate crimes. Most people witnessing same-sex PDA do not become violent despite small stress response. Response possibly due to societal socialization of same-sex affection as disgusting. Study first of its kind using salivary alpha-amylase on 120 men. Needs replication with larger samples, women, and other couple types like female same-sex or interracial.