A wide-bandpass monochromator and fast detector system at the new IBM/MIT beamline X-20C at the National Synchrotron Light Source allow the collection of X-ray scattering patterns within milliseconds. The monochromator incorporates artificial multilayers rather than crystals, and provides a flux of 1 × 1013 photons/s at 6 keV with an energy resolution of ΔE E = 1.1 × 10-2 fwhm. The detector system is based on a linear photodiode array. Using this beamline, we have carried out in situ time-resolved X-ray scattering studies of the initial kinetics of crystallization, phase separation, and ordering at time scales orders of magnitude faster than previously possible for such nonrepetitive processes. © 1988.