We studied the interactive effects of pCO2 and growth light on the coastal marine diatom Thalassiosira pseudonana CCMP 1335 growing under ambient and expected end-of-the-century pCO2 (750 ppmv),and a range of growth light from 30 to 380 μmol photons·m-2·s-1.Elevated pCO2 significantly stimulated the growth of T.pseudonana under sub-saturating growth light,but not under saturating to super-saturating growth light.