Considering recent findings that breathing influences cognitive processes, two experiments explored the relationship between breathing and visuo-spatial attention. In Experiment 1, a lateralized probe detection task was inserted into the breathing cycles of 21 healthy adults to probe effects of breathing on the distribution of spatial attention. In Experiment 2 (N = 26), the Posner cueing task measured breathing-contingent detection speed for lateralized probes after endogenous or exogenous cueing. We consistently found faster responses for left probes after exhalation and for right probes after inhalation in both experiments. Breathing also affected the speed of re-alignment of spatial attention after invalid cueing in Experiment 2. This novel breathing bias shows that our ability to encode visuo-spatial information systematically fluctuates during breathing.