Three antibiotics carbenicillin, claforan, and timentin were evaluated for their effects on the frequency of embryos forming calli, callus growth, the frequency of calli forming adventitious shoots, and the mean number of regenerated adventitious shoots per piece of organogenic callus in three loblolly pine (Pinus taeda L.) families. Of the antibiotics administered, carbenicillin maximally increased the frequency of embryos forming calli and growth rate of calli, timentin minimally increased the frequency of embryos forming calli and growth rate of calli, in comparison with antibiotic-free treatment. Compared with the control, claforan maximally increased the frequency of calli forming adventitious shoots and timentin maximally increased the average number of regenerated adventitious shoots per piece of organogenic callus, carbenicillin minimally increased the frequency of calli forming adventitious shoots and the average number of regenerated adventitious shoots per piece of organogenic callus, in three loblolly pine families tested. All three antibiotics increased the frequency of embryos forming calli and the frequency of calli forming adventitious shoots confirmed that there is a beneficial effects of antibiotics tested here on loblolly pine callus growth and shoot regeneration and, consequently, their reliability for use in the transformation of this species. This investigation could be useful for optimizing genetic transformation of loblolly pine and other conifers.