This article critically examines whether, and how, five United Nations human rights treaty monitoring bodies deal with situations in which human rights have been interfered with by non-State actors. The article uses the concepts of ‘direct’ and ‘indirect’ horizontal effect of international human rights law. An in-depth comparative analysis reviews the monitoring bodies’ general comments and views on individual communications from the bodies’ establishment until August 2017. The analysis identifies very limited evidence of ‘direct’, and two main kinds of ‘indirect’ horizontal effect of human rights applied by the bodies. First, it finds that while the bodies do engage with the ways in which non-State actors can interfere with human rights, they predominantly focus on the positive and procedural obligations of States. Second, it finds that where non-State actors are sufficiently ‘State-like’ in their nature and actions, they may be re-categorised as public actors for the purposes of human rights.