It is a long-standing assumption that holotropic breathwork (HB) induces an altered state of consciousness. However, this assumption has not been empirically tested. Consequently, 32 participants were recruited for the present study, which aimed to use the Phenomenology of Consciousness Inventory (PCI) to quantify the pattern of phenomenological subsystems and Altered State of Awareness (ASA) scores associated with a HB condition relative to a comparison condition and a baseline assessment. The hypothesis that the HB group would report a different pattern of relationships among phenomenological subsystems relative to the comparison condition and baseline was partially supported. In addition, the hypothesis that, while controlling for baseline, the HB group would report higher ASA scores than the comparison group was supported. Finally, for the HB group, transliminality did not significantly improve the prediction of ASA, while controlling for baseline. Various suggestions for future research are discussed.