There is a need to find a technique for analysing the intracellularconcentra-tions of carbon, nitrogen and phosphorus in single phytoplanktoncells growing in natural communities. Laboratory experiments with uni-algalcultures have shown that the carbon (C): nitrogen (N): phosphorus (P)ratios under balanced nutrients conditions is species-specific and do notalways follow the Redfield ratio. In this study we apply a method using aNMP-technique to measure the concentration of C, N and P in single cells ofthe three brackish-water cyano-bacteria species Anabaena sp., Nodulariaspumigena and Aphanizomenon cf klebahnii. The concentrations of C-, N- andP were also analysed by conventional methods and comparison was made withthe results obtained from the NMP-technique. Anabaena sp. showed no significant difference regarding the C-, N- and P- concentration with the two methods. In the case of N. spumigena and A. cf klebahnii the C, N and P concentrations showed approximately a 50% higher and a 50% lower concentration respectively with the NMP technique than theconvential methods. Except for the N/P ratio for A. klebahnii, the C/N-,N/P-, and C/P ratios for all three species showed no significant differencebetween the two techniques. From our results it can be concluded that theuse of NMP could be a useful tool for studying the elemental composition insingle phytoplankton species in the field.