To examine the potential role of lactate as a signalling molecule in skeletal muscle, we performed global gene expression analysis of the mouse gastrocnemius muscle, 3 h after lactate administration using the Affymetrix GeneChip system (Affymetrix, Santa Clara, Calif., USA). Among the top 15 genes with the largest fold change, increased expression of Ppargc1a, Pdk4, and Ucp3 was confirmed using real-time quantitative polymerase chain reaction. Our findings suggest that lactate serves as a signal for upregulating genes related to mitochondrial function.