[Show abstract][Hide abstract] ABSTRACT: Paphiopedilum callosum seedlings were grown on half strength macro-and micro-elements of Murashige and Skoog (1962) (1 / 2 MS) medium supplemented with cytokinins 6-benzylaminopurine (BAP) and 1-phenyl-3-(1,2,3-thiadiazol-5-yl)-urea (TDZ) alone or in combination with auxin, 2,4-dichlorophenoxyacetic acid (2,4-D). Three months after incubation, shoots in the medium with 0.5 µM TDZ produced 1.6 ± 0.40 shoots/explant. In addition, it was found that 1 / 2 MS medium without plant growth regulators produced more roots (1.80 ± 0.20) per shoot and longer roots (30.40 ± 8.04 mm) than 1 / 2 MS with 0.5 µM TDZ combined with 50 µM 2,4-D. The 1 / 2 MS medium with BAP at 10 and 50 µM resulted in 2.30 ± 1.42 and 2.20 ± 1.03 shoots/explant, while 1 / 2 MS medium without plant growth regulators resulted in 100% root induction with an average 3.70 ± 0.62 roots/explant and mean root length 34.01 ± 4.87 mm. Overall, BAP appeared to elicit the best shoot multiplication in response with P. callosum shoot explants compared with either 2,4-D or TDZ. The combined effects of TDZ and BAP may be worthwhile investigating in future shoot proliferation experiments. Root induction appeared to be restorable if TDZ is removed and BAP reduced, as the presence of BAP at the lower concentrations tested did not appear to completely inhibit root induction (unlike TDZ). Hopefully, the current study will assist with future development of ex situ conservation methods with endangered Thai orchids.