Microorganisms for hydrocortisone and prednisolone production were screened and isolated from soil samples located in five different sites i.e. rice, vegetable, bamboo, Solanum laciniatum, Ait, and medicinal plant fields in Chiang Mai province, Thailand. The proper soil dilution was found to be 1:10 for fungi and 1:10(3) for bacteria. The diluted soil samples in media were incubated at 28 +/- 2 degrees C for 7-10 days. From the 160 soil samples taken, the fungi which gave hydrocortisone production potential were Cunninghamella blakesleeana SRP I (Steroid Research Project I) and SRP II, whereas the bacteria which showed prednisolone production ability were Bacillus sphaericus SRP I, SRP II and SRP III. The highest hydrocortisone production yield found was 61.90 +/-2.90% by C. blakesleeana SRP I in a jar fermenter at pH 6.2, 24 +/- 1 degrees C, 220 rpm after a 4 day incubation. For prednisolone production, the highest yield was 66.98 +/- 0.98% by B. sphaericus SRP I in a shake flask at 30 +/- 1 degrees C, 220 rpm after 1 day incubation.