Circulat is a systemic standardized plant extract formulation that was developed for the prevention of severe manifestations of type 2 diabetes such as necrotic damage of the plantar foot. With the aim of revealing the molecular mechanisms underlying Circulat's biological activity, the effects of Circulat treatment on gene expression levels were examined in the cultured human fibroblast cell line MRC-5 using Affymetrix oligonucleotide microarrays. The analysis identified 187 genes, the expression levels of which underwent significant changes upon Circulat treatment. These include four genes (IL6, HMGA1, SLC19A2 and C4A) that have been implicated previously in the development of diabetes. A large proportion of the identified genes are involved in energy metabolism, protein synthesis, glucose metabolism and signaling pathways. Synergistic action of the Circulat components has also been revealed. Prospective applications of microarray analysis in phytopharmacology are discussed. Copyright © 2007 John Wiley & Sons, Ltd.