Amino acids essential for the growth of N. lugens nymphae were investigated. Insects were fed on the synthetic diet MED-1 lacking one amino acid from immediately after hatching. All the N. lugens nymphae were able to develop into adults in the absence of any one of the amino acids; therefore no single amino acid is essential for their growth. Growth, hawever, was markedly delayed in a diet lacking either cysteine, histidine or methionine. The insects developed into adults even when reared on a diet containing neither cystine or cysteine, but all died at the 1st instar when cystine, cysteine and methionine were eliminated from the diet at the same time.