The use of detergents for the structural study of membrane proteins is discussed with an emphasis on practical issues relating to membrane solubilization, protein aggregation, detergent purity and detergent quantitation. Detergents are useful reagents as mimics of lipid bilayers because of their self-assembling properties, but as a result, they have complex properties in solution. It can be difficult to maintain a solubilized membrane protein in a native conformational state, and the non-specific aggregation of detergent-solubilized proteins is a common problem. Empirical "stability screens" can be helpful in choosing which detergents, and which detergent concentrations, may be optimal for a given system.