Rather than merely a nuisance, noise in biological systems is a useful property. Before patch-clamp methods were invented, analysis of membrane current noise provided the first solid, if indirect, evidence for the existence of ion-conducting pores with discrete conductance levels. Although supplanted by single-channel recording techniques for most tasks, analysis of current membrane noise remains useful for certain problems, such as determining the properties of channels with rapid kinetics that open with a high probability and desensitize, channels localized at synapses, channels with an unusually low unitary conductance and open-channel noise. In addition, the role of noise in information processing in the CNS is increasingly being recognized. In this article, we summarize the analysis of current membrane noise with an emphasis on what the technique is still useful for, and discuss the role for noise in information processing.