A quick and reliable test was developed to measure the cyclization activity of cyclodextrin glycosyltransferases (CGT). Since the reproducibility depends mostly on the nature of the substrate, maltotriose was employed. The cyclodextrins formed are measured directly in situ by complexation with methyl orange and by recording the change of absorbance photometrically. The test was successfully used with CGT from Klebsiella pneumoniae M5 al and CGT from alkalophilic Bacillus. [on SciFinder (R)]