COBRA-3M, a modified version of COBRA computer code, is most suitable for the analysis of thermal-hydraulics in small pin bundles commonly used in in-reactor or out-of-reactor experiments. It includes detailed thermal models for the fuel pins and duct walls. It can handle nonuniform power distribution across the bundle and/or within a fuel pin. Temperature dependence of material properties and fuel-cladding gap conductance can be treated. Heat generation in the duct walls and the effect of heat loss to the surroundings can also be simulated. COBRA-3M has been used extensively in the design and analysis of TREAT and SLSF experiments.