P>In terms of fish production, sperm activating substances are important in the controlled insemination. This holds also for salmonids, when being provided with an agent that energizes the spermatozoa. In this study two amino acids (l-glutamate and glycine) were evaluated in their effect on sperm motility and fertilizing capacity for rainbow trout (Oncorhynchus mykiss) spermatozoa. Different concentrations of l-glutamate and glycine were added to the sperm medium (T(1) = 0.075 g per 100 ml of l-glutamate; T(2) = 0.3 g per 100 ml of glycine; T(3) = 0.075 g per 100 ml of l-glutamate + 0.3 g per 100 ml of glycine). A control treatment was also performed without the two amino acids. Results show the capacity of l-glutamate to increase the time period of sperm motility (s) significantly in comparison to other treatments, registering a maximum motility time of 57.7 +/- 10.8 s. For fertilization issue, the results do not show significant differences, being the highest value for T(1) = 98 +/- 4.5%.