To investigate copepod nauplii ingestion rates on phytoplankton, we have adapted the traditional gut fluorescence technique as it can be used with lower gut pigment concentrations. With the improved technique, laboratory experiments were performed to estimate functional responses for nauplii of Calanus helgolandicus and Centropages typicus. Nauplii were raised from eggs to copepodites and the experiments were performed with stages NIV-NV. Gut evacuation rates and ingestion rates were measured on Isochrysis galbana at different concentrations. Specific ingestion rates ranged between 0.038–0.244 μg C μg-1 nauplii C d-1 for C. typicus and 0.041–1.412 μg C μg-1 nauplii C d-1 for C. helgolandicus. Both species showed a type III functional response, reaching a saturation concentration at around 600 μgC l-1 for C. typicus and 800 μgC l-1 for C. helgolandicus.