The human gene SLC34A2 encodes NaPi-2b which is abundantly expressed in lung and to a lesser degree in epithelia of other tissues including small intestine, pancreas, prostate, and kidney. In the lung, SLC34A2 is expressed only in alveolar type II cells, which are responsible for surfactant production, so it is proposed that it uptakes liberated phosphate from the alveolar fluid for surfactant production. SLC34A2 cotransports divalent phosphate (HPO4(2-)) with three Na+ ions (electrogenic transport) from the extracellular region into alveolar type II cells. Defects in SLC34A2 can cause pulmonary alveolar microlithiasis (PALM; MIM:265100), a rare disease characterised by the deposition of calcium phosphate microliths (tiny, roundish corpuscles) throughout the lung. Most patients remain asymptomatic for years or decades, the disease following a long-term, progressive course resulting in slow deterioration of lung functions. PALM can result in a potentially lethal disease (Yin et al. 2013, Ferreira Francisco et al. 2013, Whitsett et al. 2015).