Niacin induces peripheral vasodilatation via prostaglandin D (PGD) and E (PGE) release by Langerhans cells in skin. We evaluated if niacin alone or in combination with PGD and PGE alters expression of heat shock proteins (HSP) 27 and 70. Bovine mammary epithelial cells (BMEC) were cast in collagen in 24‐well plates containing growth media (GM) composed of DMEM/F‐12, insulin, EGF, IGF‐I, BSA and antibiotics at 37°C, 5% CO2. Cultures grew into ductal structures with media changes at 48 hr intervals. On day 8 cultures were divided into Controls (C) receiving GM, GM with niacin (0.5, 1.0, or 10.0 mM), PGD2 (10 or 24 uM), PGD2 with PGE1 (both at 24uM) alone or in combination with niacin. Half were placed into incubators at 37°C (TN) and the remainder at 42°C (HS) for 8 h. At 0h and 8h, replicates were pooled, placed in TRIzol and stored at −80°C until extracted for RNA. Isolated RNA was reverse transcribed into cDNA. Expression of HSP's‐27 and 70 was measured by q‐ PCR. Addition of PGD increased HSP‐27 and 70 gene expression in HS, (P<.0001). Peak fold increases in HSP‐70 expression at 8 hr over time zero differed between C and PGD, (−2.4 vs. 9.3, P<.0001) and were greater for Hsp‐27 (−115 vs +10, P<.0001). Addition of PGE increased HSP‐27 and 70 expression compared to C and PGD alone (P<.05). We conclude that niacin with PGD or PGD+PGE alters HSP‐27 and Hsp‐70 gene expression in BMEC during HS.