ABSTRACTDinoflagellates have substantially lower growth rates than other taxa of similar size. These low growth rates have been suggested to reflect the lower chlorophyllato carbon ratio (Chla:C) in dinoflagellates, but that speculation has never been widely tested. This study tests if the variations in growth rates among taxa are related to differences in Chla:C using published data. I collected 92 data entries from the literature representing 31 species, mostly from two divisions (Chrysophyta and Pyrrophyta), and found a significant relation(r2=0.39) between growth and Chla:C. Since Chla:C is almost independent of C content, I also developed a growth model using both C and Chla:C. Together, the two variables explain 68% of variation in algal growth. However, a further 6.4% of the variance in growth can still be attributed to phyletic differences. Low Chla:C is only a partial explanation for the low growth rates of the dinoflagellates.