Diffusion-time distribution analysis ͑DDA͒ has been used to explore the plasma membrane fluidity of multidrug-resistant cancer cells ͑LR73 carcinoma cells͒ and also to characterize the influence of various membrane agents present in the extracellular medium. DDA is a recent single-molecule technique, based on fluorescence correlation spectroscopy ͑FCS͒, well suited to retrieve local organization of cell membrane. The method was conducted on a large number of living cells, which enabled us to

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... a detailed overview of plasma membrane microviscosity, and plasma membrane microorganization, between the cells of the same line. Thus, we clearly reveal the higher heterogeneity of plasma membrane in multidrug-resistant cancer cells in comparison with the nonresistant ones ͑denoted sensitive cells͒. We also display distinct modifications related to a membrane fluidity modulator, benzyl alcohol, and two revertants of multidrug resistance, verapamil and cyclosporin-A. A relation between the distribution of the diffusion-time values and the modification of membrane lateral heterogeneities is proposed.