Deranged function of the WNK1 and WNK4 (With No K) kinase isoforms result in pseudohypoaldosteronism type II (PHAII), a monogenetic disorder featuring hyperkalemia, hypertension and hypercalciuria. Mechanisms linking defective WNK function with hyperkalemia and hypertension have been widely studied, little is known about the role of these kinases in the control of Ca2+ homeostasis. The present study aimed to clarify the function of WNK1 and 4 in regulating the epithelial Ca2+ channel TRPV5 that colocalizes with the WNK isoforms along the distal nephron. To this end TRPV5 has been expressed with or without WNK1 and 4 in Xenopus oocytes and TRPV5 activity estimated from TRPV5 mediated Li+ currents. Moreover, TRPV5 protein abundance has been determined by chemiluminescence. As a result WNK4 but not WNK1 stimulated TRPV5 activity by enhancing its plasma membrane expression. WNK4 kinase activity is required for the observed effect as kinase-dead WNK4 mutant was not capable to upregulate TRPV5. To date four discrete WNK4 PHAII-causing mutations (E562K, D564A, Q565E, R1185C) have been identified. TRPV5 activation was not altered upon coexpression of WNK1 consistent with the observation that patients carrying WNK1 mutations do not have hypercalciuria. The experiments demonstrate the significance of WNK4 in TRPV5 regulation and provide a mechanism which is likely to participate in the genesis of hypercalciuria observed in some patients with PHAII.