The nitrogen conteny of the protein in pollen samples from 21 species was calculated from the amino-acid compositions of whole-pollen hydrolysates. The mean recovery of protein nitrogen in the hydrolysates estimated by comparison with Kjeldahl determinations, was 80% (SD =6%). Of the recovered nitrogen 10.7% (SD = 1.4%) was present as ammonia; since this probably originates from the deamination of asparagine or glutamine, the ammonia nitrogen was counted as protein nitrogen in the calculations. The mean nitrogen content of the pollen protein was 18.0% (SD = 0.5%). Calculations from previously published amino-acids analyses of pollens - which unfortunately do not include figures for ammonia - agree with the new data if ammonia nitrogen is excluded. It is recommended that a factor of 5.6 (=1/0.18) be used for calculating the crude protein content of pollen samples from the results of Kjeldahl nitrogen determinations.