In 1987 to 1989 the composition was studied of the nitrogen compounds (nitrogen and free amino acids) in the fruit juice of Persian lime during its commercial harvesting period. Adult Persian lime trees grafted on Citrus macrophylla and C. volkameriana were used, planted on a groundwater-affected red ferrilytic soil in the La Habana Province. Determination of the total nitrogen and of the free proline was carried out in May to July of each experimental year. The amino acid spectrum was established from juice samples in May 1987 and in July 1988. With the nitrogen concentrations varying between 14 and 90 mg/100 ml of juice, no consistent behaviour or pattern could be detected either in the total nitrogen content or the proline content in the juice during the 3 experimental years. 14 free amino acids were found, with about 90% of the total content formed from asparagine acid, glutamic acid, alanine, proline, gamma-aminobutyric acid, and arginine, regardless of the experimental year or the grafting basis.