The invention provides a method for determining whether a human immunodeficiency virus is resistant to a viral entry inhibitor. The methods are particularly useful for determining resistance to inhibitors that act by a non-competitive mechanism. In certain aspects, the methods comprise determining whether an HIV population is resistant to an HIV entry inhibitor, comprising determining a log-sigmoid inhibition curve comprising data points for entry of the HIV population in the presence of varying concentrations of the HIV entry inhibitor, wherein if the entry of the HIV population cannot be completely inhibited by the HIV entry inhibitor, the HIV population is resistant to the HIV entry inhibitor.