Introduction: Treatment of human polymorphonuclear leucocytes(PMN) with 1mM cycloheximide (CHX) rapidly (4 hr) results in morphologic apoptosis, internucleosomal chromatin fragmentation and loss of multiple PMN functions. These CHX effects are inhibited by cyclic-AMP (cAMP). Intracellular free calcium ([f Ca]) is an important second messenger in multiple PMN functions and is altered during apoptosis in several model systems. We examined whether resting and/or formyl peptide (FMLP)-stimulated[f Ca] in PMN were altered by CHX exposure and if these effects were blocked by cAMP. Methods: PMN were purified from healthy donors, loaded with 2 nM Fura-2AM, incubated for 1 hr, meticulously washed and reincubated from 10-240 minutes with or without CHX. Effects of 500μM of 8-4-Chlorophenylthio-cAMP (8CPT-cAMP) were examined at 120 minutes. Cells were examined spectrofluorometrically and both resting and FMLP-stimulated [f Ca] were calculated. Paired t-test of the logged data was used for statistical analysis. Results: CHX exposure did not alter resting PMN [f Ca] over 4 hr of exposure (4 hr control (CT): 37±10 nM [mean±SE] vs 4 hr CHX: 40±9 nM, both n=4, p=NS). 8CPT-cAMP significantly reduced resting[f Ca] at 2 hr of CHX exposure (2 hr CHX: 77±13 nM vs 2 hr CHX+8CPT-cAMP: 54±10 nM, both n=6, p<0.02). FMLP increased[f Ca] in control cells, and this effect was decreased by 2 hr CHX exposure (2 hr CT: 169±12 nM vs 2 hr CHX: 133±14 nM, both n=5, p<0.04). At 2 hr, 8CPT-cAMP did not block the CHX effect on FMLP-stimulation (2 hr CHX: 78±13 nM vs 2 hr CHX+8CPT-cAMP: 88±10 nM, both n=6, p=NS). Conclusions: 1) Changes in calcium metabolism in CHX treated PMN require ≥2 hr to appear and these effects are not reversed by cAMP exposure. 2) cAMP and CHX-induced[f Ca] effects are different. 3) Because cAMP both decreases resting [f Ca] and inhibits morphologic apoptosis in CHX-treated PMN, low resting [f Ca] may be associated with delay or inhibition of apoptosis.