Free amino acids in serum were monitored in 7 dairy cows during the last 20 days before parturition and for 90 days after parturition. At calving time, concentrations of Val, Lue, Ile, Trp, Ala, Pro, Tyr, Asn, Asp, and Urn decreased significantly below late-pregnancy levels. They increased significantly after parturition and into early lactation(Type 1). Concentration of Gly and Ser in serum increased from late pregnancy to early lactation(Type 2). At calving time, concentrations of Met, Phe, Lys, Arg, Thr, and Glu in serum decreased below late-pregnancy levels. There was no difference, however, in the early lactation period(Type 3). Concentrations of His and Gln in serum decreased from after parturition to the early lactation period(Type 4). Thus, transition of amino-acid concentrations during the peri-parturient period falls into 4 types. These changes probably result from the intermediary metabolites of gluco-neogenesis, feed intake, and body-tissue metabolism. Measurement of free amino acids in serum may be useful in evaluating cows' peri-parturient nutritional status.