Gas holdup was measured by an isolating technique in a continuously operating column (10 cm in diameter and 447 cm in height) under simulated flotation conditions. The effect on gas holdup of solid particle concentration (0-15% v/v), size (95% <53 mu m, 75% >53 mu m) and type (hydrophilic, hydrophobic) was investigated. In all cases, the presence of solids significantly decreased the gas holdup, the effect increasing when solids concentration increased and particle size decreased.