The importance of voltage-activated calcium channels in pain processing has been suggested by the spinal antinociceptive action of blockers of N-and P/Q-type calcium channels as well as by gene targeting of the ␣1B subunit (N-type). The accessory 3 subunits of calcium channels are preferentially associated with the ␣1B subunit in neurones. Here we show that deletion of the 3 subunit by gene targeting affects strongly the pain processing of mutant mice. We pinpoint this defect in the pain-related behavior and ascending pain pathways of the spinal cord in vivo and at the level of calcium channel currents and proteins in single dorsal root ganglion neurones in vitro. The pain induced by chemical inflammation is preferentially damped by deletion of 3 subunits, whereas responses to acute thermal and mechanical harmful stimuli are reduced moderately or not at all, respectively. The defect results in a weak wind-up of spinal cord activity during intense afferent nerve stimulation. The molecular mechanism responsible for the phenotype was traced to low expression of N-type calcium channels (␣1B) and functional alterations of calcium channel currents in neurones projecting to the spinal cord.Voltage-activated calcium channels represent a family of ionic channels that play a crucial role in the nervous system by controlling membrane excitability and neurotransmitter release. Neurones express L-, N-, P/Q-, and R-type calcium channels, which are composed of the pore-forming subunit ␣1 and the accessory subunits , ␣2␦, (1, 2) and probably ␥ (3). The importance of ␣1D (L-type), ␣1B (N-type), ␣1A (P/Q-type), and ␣1E (probably R-type) for the function of the nervous system in vivo is underlined by recent studies with genetically engineered mice (4). By contrast, the in vivo function of the four known  subunits (1, 2, 3, 4) of calcium channels is less understood. In heterologous expression systems,  subunits are required for the functional expression of ␣1 subunits (5-7), enhance the current density, and shift the voltage dependence of the activation and inactivation of recombinant calcium channels (8 -11). Additionally,  subunits have been implicated in the modulation of calcium channels by G proteins (12-14). In vivo, the expression of  subunits is modified in pathological states such as cardiac dysfunction (15) and diabetes (16). A natural occurring mutation of 4 is associated with ataxia and absence seizures in lethargic (lh/lh) mice, and this mutation modifies N-and P/Q-type calcium channels in the brain (17). The targeted disruption of 1 is lethal (18). In sympathetic neurones of 3-deficient mice, N-and L-type calcium channel currents are reduced, the activation of P/Q type calcium channels is altered, and no difference appears concerning inhibitory effects of norepinephrine on calcium channel currents (19). Such alterations of calcium channel currents in sympathetic neurones might be related to the cardiovascular phenotype of mice lacking the 3 subunit (20). Yet, the in vivo functions of the 3 subunit of ...