Improved time resolution of kinetic cellular events in flow cytometry is demonstrated by using a coaxial flow-mixing device integrated within a flow-injection (FI) system. The instrument is used in combination with a Becton Dickinson FACS Analyzer for on-line reagent addition, rapid sample mixing, and temperature control of cell suspensions. The coaxial flow device can instantaneously (< 60 ms) mix reagent and sample streams, allowing cytometric analysis of subsecond events to be performed. Kinetic measurements can be performed on the FACS analyzer in a variable time range of from 100 ms to 3 min. The system also allows the collection of unlimited cellular events at a specific incubation time point. Because the system operates continuously and no boost in core flow is required, disturbances of flow conditions are avoided. The capabilities of the flow injection cytometer have been demonstrated by the determination of internal [Ca2+]i mobilization in Jurkat T lymphocytes perfused internally with INDO-1 and stimulated by ionomycin.