PARTXTION COEFFICIEXTS OF PEXICILLINS WM o-ahres for eight penicillins have been measured by a reversed-phase thin-Rayr chrrom~atogmph~ system using w-octanol as the stationary phase. There is a nnezaur perfect tinear rellation between the X .I[ values measured at pH 3 or pH 4 and tltne kqgaritlimn-of the partition coefficients of the penicillin free acids between gr-octanol aLund O.-a&r_ Tltre clh~ange o6' R~I with change in pH of the developing buffer is close to a tRneoretiicc;Un vaJk for measurements at pH 3 and 4, but it is too low for measurements aUppI~alxmaI~-_M~en~ttion~ is drawn to' an unusually low-HASSCEI z value for the methyl group off phteHnetnlli~u, Severali biikgical properties of penicillins have been shown'3 to be quantita-tiveJy OH qunatllihat.iveRy related to their partition coefficients. BIAGI et al.1 have used WJV vallunes ffrom a~ thin-layer chromatographic (TLC) system for correlation of anti-lI+tie properties-BUD .XSD ~~I.A.Mw.ALL~ used calculated HAXSCEI JZ values4 and, to a IIesser extemmt, measured partition coefficients, for correlation of the extent of serum b~aE.ung of mrmamq-penicihins-Bn_xm d ~fl_~ have recently presented R;tl results from their system developed WSII lbrnfikrs of aiiifferent pH and suggested that such studies might provide a model systernn ffr investigating penetration of penicillins through biological membranes. We sltnw~ irn th.its paper that BL~GI'S results are not in accord with theory and we present ma a&ternative reversed-phase TLC system for penicillins and compare results firomln iiu wiiu.b measured partition coefficients for the same set of compounds. Gllass #&es, 201 x zo cm, were coated with a 0.5 mm layer of Camag microaq..ualllllme cenlllDJ!ose (6-,_s g to' 330 ml water) using a motorised spreader. The plates were dlried at room temperature overnight, heated in an oven at IIOO for 1.5 11, cooled