Bovine mammary epithelial (BME-UV1, clone E-T and BME-UV, clone E-T2) and myoepithelial (BMM-UV, clone m-T2) cell lines were used to study the modulation of cell-associated activity of urokinase-type plasminogen activator (u-PA), as well as mRNA transcripts of u-PA, its receptor (u-PAR), and inhibitors (PAI-1 and PAI-2) during the cell cycle. After release from a growth arrest accomplished by growth factor deprivation, the length of the cell cycle was determined as 19–21 h, with G1, S, and G2+M phases of 6–7, 7–9, and 5–6 h respectively. As the cell cycle progressed, accumulated cell-associated u-PA activity increased. Maximal activity occurred at the S/G2 boundary and decreased during the G2/M phases. All cell lines tested produced plasmin-specific inhibitor(s). Accumulation of u-PA mRNA peaked 3 h after stimulation into the growth cycle for m-T2 and E-T and during 3–6 h for E-T2 cells. Maximum levels of u-PAR mRNA were observed at 3 h for the E-T cell line, 6–9 h for E-T2 cells, and 3–9 h for m-T2 cells. The cell cycle distribution of the PAI-1 mRNA was similar to that of u-PA for both epithelial cell lines, while for m-T2 cells maximal accumulation of PAI-1 mRNA was detected at 3–9 h after growth initiation. The increase of PAI-2 mRNA transcription for m-T2 and E-T cells was detected at 3–6 h. The PAI-2 mRNA in E-T2 cells was under detectable levels. The data indicate that the expression of the constituents of the PA system in bovine mammary epithelial and myoepithelial cells is not cell type-dependent but is tightly connected to the phase of the cell cycle.