The infinite multiplication factor, k∞ is one of the basic parameters of a sub-critical assembly. Usually, these assemblies are designed for maximum k∞ however, it is difficult to conduct laboratory experiments which yield a value of k∞ to reasonable accuracy. Common methods, such as the loading technique and exponential experiment, are of doubtful validity or require apparatus not always available. Pulsing techniques are widely accepted, but are difficult to apply to reflected assemblies. In this work, an alternative approach is used. It is based on the integration of the thermal-neutron flux over the equivalent infinite medium. Use of variations in the method with poisoned assemblies eliminates the need for accurate determinations of the source strength, the absolute thermal-flux calibration, and the epithermal parameters of the medium. The theory is general and can be applied with a minimum of equipment. The results obtained from this method (and its variations) were checked by pulse measurements on the bare assembly and by a four-factor formula calculation. All results agree to within 2%.