The Drosophila Na,K‐ATPase (or sodium pump) α‐subunit gene was found to contain 10 exons and span approx. 25 kb. Two nearly adjacent transcriptional initiation sites were identified, and the 2085‐ nucleotide sequence upstream of the first transcriptional start was analysed for promoter activity in transfected Drosophila SL2 cells. This region was found to contain many cis‐acting elements that influence promoter activity, including elements that confer 2‐ to 3‐fold higher activity in SL2 cells cultured at 30°C versus 22°C. Temperature‐sensitive transcriptional regulation of the Na,K‐ATPase α‐subunit in Drosophila is a plausible mechanistic candidate for the factor driving temperature‐dependent up‐regulation of the Na,K‐ATPase α‐subunit described here for fly strains homozygous for single P‐element insertions in the α‐subunit gene. Four new P‐element insertion strains were identified in this study, each insertion site lying within the first intron of the Na,K‐ATPase α‐subunit gene. The insertion in strain 0462 resulted in cold‐sensitive recessive lethality; flies homozygous for the 0462 mutation could be rescued by growth at 29–30°C, a condition that partially corrected a deficiency in the level of Na,K‐ATPase α‐subunit. The high‐temperature rescue of homozygous 0462 flies appeared to result primarily from improved Na,K‐ATPase expression rather than an increase in the rate of ion transport per Na,K‐ATPase molecule. These observations point to a role for sodium‐pump activity in determining the range of temperature tolerance in Drosophila and demonstrate that relatively subtle changes in sodium‐pump expression can have major consequences in whole organisms.