Lignosulfonate-humate a and lignosulfonate-humate b, derived by an industrial process from lignin, were studied chemically and biologically, and their effects on maize metabolism compared with the responses induced by humic substances obtained from leonardite. Lignosulfonate-humate a and lignosulfonate-humate b elicited hormonelike activity and leonardite displayed giberellin properties. To improve our understanding of their biological action, lignosulfonate-humate a, lignosulfonate-humate b and leonardite were supplied to maize plants and their effect was studied on growth, nitrogen metabolism and photosynthesis. All products increased root and leaf growth. Glutamine-synthetase, glutamate-synthase enzyme activities and protein content were all increased. The treatments also increased chlorophyll content, glucose, fructose and rubisco enzyme activity, suggesting a positive role of lignosulfonate-humate a, lignosulfonate-humate b and leonardite in the photosynthetic process. In addition, an increase in phenol content was observed. In light of these results, being environmentally friendly products, lignosulfonate-humate a and lignosulfonate-humate b could be used to increase crop yield.