AbstractA flow field‐flow fractionation (FIFFF) system capable of accurate and reproducible flowrate programming has been assembled and tested. This modified system consists of three computer‐controllable pumps, two that regulate the incoming and outgoing cross flowrates and one that controls the channel flowrate. The system also has a computer‐linked balance that allows for instantaneous measurement of the cross flowrate. Programming of the field strength (or cross flowrate) was used to decrease the analysis time and improve detectability of late eluting peaks in FIFFF analysis. A six component latex mixture, with microspheres ranging from 20 to 426 nm in size, was used as a test material. With programming, this mixture can be separated in 8 min. © 1995 John Wiley & Sons, Inc.