The effect of three non-steroidal anti-inflammatory agents (NSAIs) and of two new pyrido-pyrimidine derivatives, CHINOIN 127 (1-6-dimethyl-4-oxo-1,6,7,8,9)a-hexahydro-4H-pyrido (1,2-2)pyrimidine-3-carboxamide) and CHINOIN 105 (1-6-dimethyl-4-oxo-1,6,7,8-tetrahydro-4H pyrido (1,2-a) pyrimidine-3-carboxamide) was compared in immune tests using human cells in vitro including T and B lymphocyte proliferation induced with mitogens, spontaneous motility of polymorphonuclear leukocytes, lymphokine (LIF) production, antibody-dependent cell-mediated cytotoxicity (ADCC) and natural killer cell (NK) activity. Indomethacin (INDO) at therapeutic concentrations enhanced the proliferation of lymphocytes stimulated by both Con A and PWM. Acetylsalicylic acid (ASA) increased proliferation of lymphocytes stimulated by Con A and at high concentration inhibited DNA synthesis induced by PWM. Phenylbutazone (PhB) increased DNA synthesis induced by PWM but not by Con A. CHINOIN 127 and CHINOIN 105 inhibited the proliferation of T lymphocytes but failed to influence DNA synthesis of B cells. Indomethacin, ASA and PhB inhibited the spontaneous motility (migration) of polymorphonuclear leukocytes. LIF production of lymphocytes was inhibited by INDO, ASA, PhB, CHINOIN 127 and CHINOIN 105. Phenylbutazone and ASA inhibit ADCC and NK. INDO, Chinoin 127 and Chinoin 105 failed to influence the effector cells of ADC and NK cytotoxicity.