The secretory pathway Ca²⁺ ATPase (SPCA) provides the Golgi apparatus with a Ca²⁺ supply essential for Ca²⁺-dependent enzymes involved in the post-translational modification of proteins in transit through the secretory pathway. Ca²⁺ in the Golgi apparatus is also agonist-releasable and plays a role in hormone-induced Ca²⁺ transients. Although the Ca²⁺ ATPase inhibitors thapsigargin is more selective for the sarcoplasmic–endoplasmic reticulum Ca²⁺ ATPase (SERCA) than for SPCA, no inhibitor has been characterised that selectively inhibits SPCA. A number of inhibitors were assessed for their selectivity to the human SPCA1d compared to the more ubiquitous human SERCA2b. Each isoform was over-expressed in COS-7 cells and the Ca²⁺-dependent ATPase activity measured in their microsomal membranes. Both bis(2-hydroxy-3-tert-butyl-5-methyl-phenyl)methane(bis-phenol) and 2-aminoethoxydiphenylborate (2-APB) selectively inhibited SPCA1d (with IC₅₀ values of 0.13μM and 0.18mM, respectively), which were of 62- and 8.3-fold greater potency than the values for hSERCA2b (IC₅₀ values; 8.1μM and 1.5mM, respectively). Other inhibitors tested such as bis-phenol-A, tetrabromobisphenol-A and trifluoperazine inhibited both Ca²⁺ ATPases similarly. Furthermore, bis-phenol was able to mobilize Ca²⁺ in cells that had been pre-treated with thapsigargin. Therefore we conclude that given the potency and selectivity of bis-phenol it may prove a valuable tool in further understanding the role of SPCA in cellular processes.