It was the aim of this study to compare the concentrations of total (TC) and free L-carnitine (FC) in blood serum of different groups of lactating cows. The animals were allotted into three groups, a) control animals (N = 11), b) cows with abomasal displacement (AD) (N = 5) and c) cows with puerperal disorders (PD) (N = 5). TC and FC were measured with an radioenzymatic assay. Blood samples were collected from 5 to 0 d before parturition (a. p.) and from 0 to 28 d after parturition (p. p.). It was of interest to examine whether L-carnitine might be limiting under certain conditions of metabolic stress which are typical for high yielding lactating cows. Concentrations of TC and FC (mumol/l) in control cows before and after parturition were 10.0* and 8.6* and 6.0-8.9 and 3.7-4.9, respectively. The corresponding TC and FC values for cows with AD were 19.6* and 8.9* and 10.5-20.7 and 4.8-6.9, respectively. Cows with PD showed TC and FC concentrations a. p. and p. p. of 15.7* and 9.2* and 10.3-13.0 and 4.8-6.3, h other puerperal disorders PD respectively (* only one value). TC and FC concentrations in serum of normal cows were higher before than after parturition. Cows, which developed post partal puerperal disorders had a higher prepartum concentrations of TC and CE, on the other hand, serum concentrations of FC was lower. Post partum cows with metabolic disorders showed higher CE levels than control animals. Cows which developed DA had significantly higher concentrations of TC and CE in serum only on d 7 p.p. than animals with other PD. It appeared that increased fat mobilization was regularly associated with responsive increases of CE concentrations in blood serum.