AMP-activated protein kinase (AMPK) is considered to be an energy-sensing key regulator of glucose and fat metabolism. This study was accomplished in order to link the expression of certain genes of muscle energy metabolism with data achieved by histomorphometry and enzyme analyses in M. longissimus of 15 Piétrain and 19 Leicoma pigs. After staining with combined ATPase/Diaphorase technique the proportion and mean fibre area of slow- and fast-twitch oxydative and fast-twitch glycolytic fibres (STO, FTO and FTG, respectively) were determined. Enzyme activities of isocitrate dehydrogenase (ICDH) and lactic dehydrogenase (LDH) were ascertained. By means of Northern analyses the mRNA expression of both a isoforms of the AMPK was analysed. In Piétrain, the expression of AMPK a1 subunit (a1) was positively correlated with ICDH activity and the percentage of STO fibre area proportion, whereas in Leicoma the expression of a1 was positively correlated with the FTO fibre type percentage. In both races a1 was negatively correlated with the proportion of FTG fibres. To confirm the data at protein level immunohistochemistry was carried out with antibodies detecting both a1 and a2 isoform of the AMPK as well as slow Myosin. The findings thus obtained indicated that the expression of AMP-activated kinase a1 subunit is strictly related to the expression of slow myosin in porcine M. longissimus.