Heterogeneous surfaces, such as solid particles, are known to efficiently increase nucleation rates during crystallisations from solution. In this work, air bubbles have been used to act as heterogeneous surfaces, to facilitate the critical nuclei formation of large protein molecules. Protein crystallisation experiments were performed using the hanging-drop method, to investigate the effects of concentrations of lysozyme and sodium chloride, and air bubbles on the nucleation of crystals. The introduction of an air bubble template resulted in an overall reduction in the nucleation induction time, over the majority of the experimental conditions. With air bubbles in the hanging droplets, the population density of the lysozyme crystals was up to 1.5 times higher than that in the droplets that contained no bubbles. For the studied experimental conditions, the mass yield was also found to increase by adding air bubbles into the droplet.