Ever since decidual cells were recognized as the source of decidual prolactin (dPRL), very few reports have dealt with the role of calcium (Ca2+) on dPRL synthesis and release. In a recent work, we described the presence of T-type Ca2+ channels in these cells, giving Ca(2+)-dependent action potentials. However, we failed to demonstrate any action of decidual cell Ca2+ modulation on acute dPRL release, but observed only long-term effects. We have now investigated these effects on decidual protein and dPRL synthesis after 24 h treatments. When Ca2+ channel blockers or EGTA (2 mM) were added to the culture medium, dPRL release and [3H] leucine incorporation into proteins decreased. Increasing external Ca2+ up to 2 mM instead of 0.8 mM or changing the external K+ concentration (30 mM instead of 5.6) had no consequence on dPRL release, whereas 2 mM of Ca2+ enhanced total protein synthesis. No toxicity was noted with these treatments. Finally a possible effect of Ca2+ modulation on dPRL synthesis was studied using [35S] methionine. The specific activity of [35S] methionine on dPRL was similar in control and treated cells (EGTA, 2 mM Ca2+, cobalt). These results support the idea that Ca2+ controls dPRL synthesis in decidual cells, acting only on general protein synthesis processes.