Elemental analysis (carbon, nitrogen and phosphorus) on 30 single cells and 6 thecae of Dinophysis norvegica collected from the Baltic Sea was performed using a Nuclear Microprobe (NMP). For each cell elemental maps were created and the cellular C, N and P content was obtained. Concentrates of D. norvegica cells (>95% purity) were simultaneously collected for toxin analyses and measurement of particulate C, N and P content by traditional methods for comparison. The traditional measurements of C, N and P yielded 2 times higher values per cell than the ones obtained by the NMP-method, nevertheless, the averages for the elemental ratios were nearly identical between the bulk measurements and NMP. Carbon per cell measured by NMP varied by a factor of 2.2 as could be expected in a growing population (267 - 583 pmol/cell). Nitrogen content varied from 6 to 38 and P from 0.6 to 2.1 pmol/cell respectively. The cells were divided into two groups: cells with N/P>16 (Redfield) (n=16) had a significantly higher average N content per cell than cells with N/P<16 (n=14). However, the two groups did not differ significantly in average P content per cell. Moreover, the average C/N ratio was significantly higher for the N/P<16 group than for the N/P>16 group, while the average C/P ratio did not differ significantly between the groups. Thus, in the studied population about half of the cells were nitrogen deficient to varying degree, while no cells could be characterized as P-deficient. The data shows that cellular nutrient status, especially cell quotas of nitrogen, can vary considerably within a population of one algal species growing under the same environmental conditions in situ.