Electrochemistry is emerging as an important technique for selective and sensitive detection in ultrasmall environments. The growth in use of electrochemical techniques can be attributed to improvements in instrumentation as well as miniaturization of the electrodes. Individual microelectrodes are being used to conduct cellular investigations in vitro and in vivo that require detection of minute amounts of material. Analyzing a sample released upon stimulation of a single cell is extremely difficult because of the sample's small volume and the femtomole (10⁻¹⁸) to zeptomole (10⁻²¹) levels of analyte present. To realize the full potential of electrochemical techniques, further developments in small-volume sample handling are needed to prevent dilution by restricting the low analyte levels present in single cells to picoliter (10⁻¹²) volumes.