Four strains of the coccolithophore <i>E. huxleyi</i> (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO<sub>2</sub> levels ranging from ~200 μatm to ~1200 μatm. Growth rate, particulate organic carbon content, and particulate inorganic carbon content were measured, and organic and inorganic carbon production calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the analysed parameters and none of the four strains displayed a response pattern previously described for this species. We conclude that the sensitivity of different strains of <i>E. huxleyi</i> to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature.