In this work, microdialysis is employed to monitor cell metabolism within engineered tissues and the technique is tested with model engineered cartilage. Bovine articular chondrocytes isolated from the metacarpalphalangeal joint were seeded evenly in an alginate gel at the densities ranging from 3.3 x 10(6) to 17.2 x 10(6) cell ml(-1), and cultured in a bioreactor for 5 days. The levels of glucose as the main cell nutrient, and the level of lactate as the main cell metabolic product, were monitored continuously in the centre of the construct using a microdialysis probe. Microdialysis probe recovery was assessed for lactate on the basis of relative loss of radioactively labelled lactate, probe fouling was determined from the relative recovery of a dye phenol red. Relative recovery of the probe fell by about 34% over the first 15 h of incubation and then remained constant. No significant probe membrane fouling was observed over the monitoring period. The fluctuation in the measurements resulted mainly from air bubbles, and was reduced by plotting the ratio of lactate to glucose concentration measured in the probe dialysate. Results show that the level of lactate in the construct centre varied with cell density, increasing as cell density increased. Addition of 12% foetal bovine serum to the nutrients supplied to the construct stimulated cell metabolism and led to an increase in lactate levels in the construct centre. (c) 2005 Elsevier B.V. All rights reserved.