Changes in the amounts of chlorophyll a, chlorophyll c, fucoxanthin, diadinoxanthin and β-carotene were determined during Phaeodactylum tricornutum growth. The transition of the culture from the logarithmic to the stationary phase is accompanied by an increase in the carotenoids: chlorophyll a ratio, associated with variations in the percentage of individual carotenoids. While fucoxanthin content decreases with the age of the culture, diadinoxanthin content increases and β-carotene remains almost constant. The furanoid isomer of diadinoxanthin, absent during logarithmic growth, appears increasingly during the nutrient-deficient period. Changes in the amounts of chlorophyll a, chlorophyll c and fucoxanthin are quite similar.Facultad de Ciencias Exactas