The patterns of 14C incorporation into the major endproducts of photosynthesis were measured in the surface waters of a New Zealand coastal upwelling system between 8 March and 5 April, 1983. Overall, the majority of 14C was incorporated into protein (x=43.4%) followed by that into polysaccharide (x=33.3%), lipid (x=18.9%) and low molecular weight (LMW) metabolites (x=4.5%). High relative accumulation of 14C into protein occurred at the expense of 14C flow into storage products (primarily polysaccharide) and, to a lesser degree, LMW metabolites. The lowest proportion of 14C incorporated into protein was generally observed in the productive waters associated with the upwelling center. The proportion of 14C incorporation into protein was positively correlated with seston particulate-N: particulate-P (PN:PP), particulate-N:chlorophyll (PN:chl) and particulate-P:chlorophyll (PP:chl) ratios, but was negatively correlated with assimilation number. Time-course experiments under constant environmental conditions revealed that the photosynthate fractions attained constant proportions in <4h. Under a natural day/night cycle the total incorporation of 14C was paralleled most closely by the 14C flow into polysaccharide, showing increases during the day and decreases at night. This pattern also occurred in the LMW and lipid fractions, although not as marked. In contrast, incorporation into protein continued during both day and night. The results of a pulse-chase experiment implied that polysaccharide was the first major product of photosynthesis and had a turnover time of about 2 h.