Escherichia coli 044 K74 was able to biotransform trans-crotonobetaine to L(-)-carnitine in continuous packed-bed reactors with cells immobilized in glass beads or polyurethane foams. Fumarate was added to the medium used for growth to increase both the carnitine production rate and carnitine yield. Although high productivities close to 2 g l(-1)h(-1) were obtained with both supports carnitine yields of 26% are still low for its large-scale application. Biotransformation rates with immobilized resting cells took place to the same extent as that with growing cells, but enhanced the carnitine yield; however after a week of continuous L(-)-carnitine production the biotransformation capacities diminished due to a progressive cell washout. The reactors with immobilized resting cells completely recovered the L(-)-carnitine production rate after feeding the systems with complex medium for 12 h. Continuous reactors with immobilized resting cells look promising for bioconversions when run under continuous production/regeneration cycles.