The potassium channel TASK-3, a member of the two-pore-domain K⁺ (K_2P) channel family, can be inhibited by acidic extracellular pH and by activation of Gq-coupled receptors and can be activated by volatile anesthetics. We have studied the mechanisms controlling the intracellular transport of human TASK-3 channels (i) by expressing wild-type (wt) and mutant channels in Xenopus oocytes and measuring TASK-3 current amplitude with the voltage-clamp technique, (ii) by attaching the C-terminus of TASK-3 to the reporter protein CD8, and (iii) by attaching the C-terminus of TASK-3 to the (truncated) C-terminus of Kir2.1. The surface expression of these fusion proteins was measured with an antibody-based luminometric assay. The C-terminus of TASK-3, which faces the cytosol, ends with the amino acid sequence MKRRKSV. This sequence contains a type-3 14–3–3 binding motif (RRxSx) and an overlapping tribasic retention signal, KRR. Removal of the last five amino acids of TASK-3 (DC5 mutant) eliminated both the binding of 14–3–3 and the retention signal. The DC5 mutant showed an approximately five-fold reduction in current amplitude and surface expression compared to wt channels. To identify sequence motifs in the cytoplasmic C-terminus responsible for the reduced current amplitude produced by the DC5 mutant we successively truncated C-terminus of TASK-3. The DC70 mutant produced about 3.5 fold more current than the DC5 mutant. The surface expression of the DC80 mutant was drastically increased compared to the DC30 mutant. Immunohistochemical staining of COS-7 cells 48 h after transfection with CD8-TASK-3 truncation mutants confirmed the increased expression of the DC80 mutant at the surface membrane. In contrast, the wt TASK-3 and the DC10 or DC30 mutant were hardly detectable at the surface membrane at this time point. These findings suggest that TASK-3 harbours additional sequence motifs in the C-terminal region DC80-C30 which are important for the regulation of the transport of the channels to the plasma membrane.