A new miniaturized micro sequential injection coupled with the lab-on-valve (mu SIA-LOV) technique was full-blown to perform inhibitory studies on dihydrofolate reductase (DHFR). The system was used to evaluate the DHFR inhibition activity of metal-based anticancer compounds. The metal complexes exhibited IC50 values in the range 1.3 +/- 0.3-108 +/- 7 mu M, with half of the complexes lying in the low mu M range, i.e., 1.3 +/- 0.3-4.4 +/- 0.2 mu M. For comparison, methotrexate (MTX), a known inhibitor of DHFR, has an IC50 value of 0.38 +/- 0.06 mu M. The mu SIA-LOV is a versatile, robust, rapid, and easy to operate, allowing automated determination of DH F R inhi-ition. Moreover, the automated system requires very little sample (approximately 40 mu L per analysis), uses minimal reagents (5 times less than the batch procedure used), and generates very little waste (around 1.2 mL per analysis) compared with batch methods, considerably reducing costs.