The station C-3 near the upwelling center at 15 ¿S off the Peruvian coast was studied during cruises from March to May during the El Ni¿o year 1976 and the non-El Ni¿o year 1977. Mean nutrient concentrations, integrated to the base of the euphotic zone, were lower in 1976 than in 1977 (86% for nitrate and 41% for silicate), although the mean surface temperatures in the two years were similar. The 1% light penetration depth was shallower in 1976. Estimates of mean in situ nitrate and ammonium uptake were lower for the El Ni¿o year by about 25% and 69%, respectively, than for the non-El Ni¿o year. The proportion of new production, f, was higher in 1976, owing to lower integrated ammonium uptake, than in 1977. Mean integrated values for carbon fixation were similar for both years. New carbon production was calculated from carbon fixation values multiplied by f and from the product of nitrate uptake and the Redfield ratio. The values agreed well, except in 1976 when the Redfield ratio calculation yielded a low value due to a distorted C/N uptake ratio, about 15 in 1976 compared to 7 in 1977. The mean of all calculated values of new carbon production was 7.74 mg-at. C m-2 h-1. The high C/N uptake ratio in the El Ni¿o year suggests a greater than normal interception of upwelled CO2 by new production with possible effects on the pCO2 gradient between the ocean and atmosphere. A compilation of the maximum values observed during comparable cruises to three upwelling areas showed maximum values of euphotic zone nitrate concentration and specific nitrate uptake to be reduced considerably during El Ni¿o years, while silicate concentrations remained relatively unchanged. ¿ American Geophysical Union 1987