Seed bioassays are employed to determine the stimulatory effect of various biological products on the seed germination of plants used for the detection and control of toxic environmental contaminants. The objective of the present study was to design an in vitro bioassay to monitor the quality of the final production of FitoMas E, a bionutrient derived from the sugar industry and produced by the Instituto Cubano de Investigaciones de los derivados de la Caña de Azúcar By-Products (ICIDCA), by determining rates of seed germination and growth of lettuce (Lactuca sativa L.) as an indicator plant. A significant effect of controllable factors under study (FitoMas E concentration in lots and replicates of Petri dishes) was determined by one-way and multifactor ANOVA analysis. In all cases, the highest values of relative germination and growth occurred at a concentration of FitoMas E of 0.1 mL L-1, with a marked increase in the growth of hypocotyl (RHG), which decreased at concentrations of 2.5 and 5 mL L-1. These results can be explained by the hormesis phenomenon, which is characterized by stimulation at low doses and inhibition at high doses. For a confidence level of P ≤ 0.05, there were no significant differences between Petri dishes with lettuce seeds and lots in all responses tested. The bioassay method implemented in this study was fast, simple and reliable.