This study was performed to evaluate the impact of phytohormones indole-3- butyric
acid and gibberellic acid (IBA and GA3) on 6 indigenous species of microalgae, isolated from
different regions in Sharkia Governorate, Egypt, in terms of their dry weight, lipids and protein
contents. Lipids were measured after ethanol-chloroform extraction, and proteins were measured by
micro-Kjeldahl method. In general, all treatments of IBA gave positive effects on biomass dry weight,
total lipids and protein contents compared to control except high level of IBA (20 mg/l medium). On
the contrary, most concentrations of GA3 gave negative results in all microalgal cultures. The increase
in biomass dry weight, total lipids and protein contents due to phytohormones treatments has reached
3.4 times in biomass, 3 times in total lipids, and 3.5 times in total protein contents. In biomass dry
weight, the highest responses were found in the Chlorella vulgaris MG14 340% to IBA treatment of
15 mg/l, followed by Chlorella vulgaris MG30 329% under the same treatment. The highest value for
each of total lipids and proteins for Chlorella vulgaris MG14 were 300% and 351%, respectively in
response to 15 mg/l treatment. In general, it is most likely that phytohormones may be considered as a
promising tool in maximizing the exploitation of microalgal cultures in biomass and biodiesel
production.