The effect of P-limitation and viral infection on prokaryotic production (PP) and respiration was determined during the early winter in the Northwestern Mediterranean Sea. Addition of P enhanced prokaryotic growth and viral production. The concentrations of total dissolved nitrogen increased linearly with decreasing viral abundance, PP and growth efficiency across treatments. Our data suggest that microbial growth can also be P-limited in winter and that viral lysis products can be readily used by prokaryotes depending on nutrient availability.