Changes in the levels of mRNAs encoding ion transporters (ATP1B1, NHE1, NKCC1), beta-actin, GAPDH, regulators of proliferation and apoptosis (p53, Bcl-2) and kinase hSGK, involved in cell water regulation, were studied using RT PCR in the peripheral human lymphocytes activated with phytohemagglutinin for 4-24 h. The common, "grouped", effect that was found was an increase in the levels of the studied mRNAs after an 8 h activation, sometimes preceded by a delay or slight decrease at the initial stage of 0-4 h. Apart from the common features, some differences were observed in the time courses and amplitudes of the responses of individual mRNAs. The arrangement of the individual mRNA responses in lymphocytes from different donors could differ significantly, thus indicating differential regulation of the studied mRNAs apart from the "grouped" effect. The data obtained confirmed our suggestion that regulation of ion transport at the level of mRNA could be involved in the changes of ion balance at the late stage of lymphocyte activation.