Flow cytometry is now a well established technique in cell biology and is gaining increasing use in clinical medicine. The major applications to date in the latter have been in DNA histogram analysis to determine “ploidy” (DNA index, Hidderman et al. 1984) and S-phase fractions for prognostic purposes in cancer patients and in immunophenotyping (Parker 1988). However, more recent applications in cancer work include determination of tumour cell production rate using bromodeoxyuridine (Begg et al. 1985) and estimations which relate to therapy resistance including glutathione, drug efflux mechanisms and membrane transport (Watson 1991). The power of the technology relates to its capacity to make very rapid multiple simultaneous measurements of fluorescence and light scatter at the individual cell level and hence to analyse heterogeneity in mixed populations.

The early commercial instruments were somewhat fearsome beasts with vast arrays of knobs, switches, dials, oscilloscopes and wires hanging out all over the place. At best, they tended to be regarded as “user non-friendly” and at worst as “non-user friendly”. However, the recent generation of machines have been simplified considerably, with the in-house computer taking over many of the tasks which the operator previously had to perform manually. The undoubted “user-friendliness” of these modern instruments, together with the relative reduction in initial capital outlay, is a considerable advantage as it makes the technology available to many more users.