An identification of the environmental factors regulating the biosynthesis of antibiotics by fluorescent pseudomonads is an essential step toward improving the ability of these bacteria to control plant pathogens. Investigation of nine fluorescent pseudomonads, utilized in growth suppression of Rhizoctonia solani, the causal agent of root rot and damping-off of bean plants, by the method of HPLC showed that the three isolates Pf-100, Pf-101 and Pf-68 were able to produce pyoluteorin (Plt), 2,4-diacetylphloroglucinol (DAPG) and monoacetylphloroglucinol (MAPG). Study of the influence of different liquid cultures and time on DAPG production revealed that in KB only Pf-100 and in KBG as well as in YM all the three isolates produced DAPG with the antibiotic concentration being different depending on time past. GCM medium stimulated DAPG production in Pf-101 and Pf-68 within 24 h. MAPG production on KBG was detected in Pf-68 and Pf-101, while on YM all the three isolates produced MAPG with its production decreasing with the passage of time. KB stimulated Plt production by the three isolates and the antibiotic concentration reached its maximum levels at 24, 72 and 96 h for Pf-100, Pf-101 and Pf-68, respectively. Plt production was stimulated in KBG growth medium in all the three isolates but its concentration was lower than that in KB.