Concentrations of free and bound proline and total free amino acidswere measured in the organs of field bean (cv. Minica), grown under field conditions. The very young seeds of 95-day-old plants had a very high content of more than 1mg free proline per gram fresh weight. The free proline content of leaves and pod walls did not exceed 0.1 mg per g fresh weight. The ratios of free proline and total free amino acid concentrations in the different organs were not constant during the development of the plants. The ratio of the free and bound proline concentrations was very high by the time the youngest seeds and pod walls were sampled and decreased rapidly during the further process of ripening to a value which was comparable to the ratios of the other organs. This very high ratio was not a consequence of a water shortage. It is therefore suggested that free proline has a characteristic function in the development of the generative organs.