Studies on the bulk catecholamine release from fetal and neonatal rat adrenals, adrenal slices, or isolated chromaffin cells stimulated with high K⁺, hypoxia, hypercapnia, or acidosis are available. However, a study analyzing the kinetics of quantal secretion is lacking. We report here such a study in which we compare the quantal release of catecholamines from immature rat embryo chromaffin cells (ECCs) and their mothers' (MCCs). Cell challenging with a strong depolarizing stimulus (75 mM K⁺) caused spike bursts having the following characteristics. ECCs released more multi-spike events and wave envelopes than MCCs. This, together with narrower single-spike events, a faster decay, and a 3-fold smaller quantal size suggest a faster secretory machinery in ECCs. Furthermore, with a milder stimulus (25 mM K⁺) enhanced Ca²⁺ entry by L-type Ca²⁺ channel activator BayK8644 did not change the kinetic parameters of single spikes in ECCs; in contrast, augmentation of Ca²⁺ entry increased spike amplitude and width, quantal size and decay time in MCCs. This suggests that in mature MCCs, the last exocytotic steps are more tightly regulated than in immature ECCs. Finally, we found that quantal secretion was fully controlled by L-type voltage-dependent Ca²⁺ channels (VDCCs) in ECCs, while both L and non-L VDCCs (N and PQ) contributed equally to secretion control in MCCs. Our results have the following physiological, pharmacological, and clinical relevance: (1) they may help to better understand the regulation of adrenal catecholamine release in response to stress during fetal life and delivery; (2) if clinically used, L-type Ca²⁺ channel blockers may augment the incidence of sudden infant death syndrome (SIDS); and (3) so-called Ca²⁺ promotors or activators of Ca2+ entry through L-type VDCCs may be useful to secure a healthy catecholamine surge upon violent stress during fetal life, at birth or to prevent the SIDS in neonates at risk.