Abstract: Different field and pot trials were conducted to evaluate the effect of an auxin precursor, L-tryptophan on the growth and yield of rice, wheat, soybean, potato and tomato. Rice (cv. Basmati-385) seedlings treated with 10–2-10–5 M and 10–1-10–5 M L-TRP by dipping seedling roots in respective solutions for one hour gave maximum paddy yield and number of panicles per hill at 10–5 M, 10–2 M and 10–1 M L-TRP levels in different field trials. L-Tryptophan (10–4 M) significantly enhanced grain yield and 1000-grain weight of wheat (cv. Inqlab) in a field trial. Total biomass and grain yield in case of soybean (cv. William) were found maximum with 10–2 M L-TRP, fresh weight of tubers and yield of potato (cv. CEB 819-17) were observed at the highest value with 10–5 M L-TRP and number of fruits per plant and yield of tomato (cv. 366-87 Pakit) were at peak when treated at 10–4 M L-TRP in pot trials. In nutshell, L-tryptophan application to different crops significantly increased all the yield components. The data collected from different crops was subjected to Dunnett's test.