A low-pressure liquid chromatographic method on silica gel 60, with chloroform containing 0-1% (v/v) of methanol as eluent, is described that allows the isolation of isorhoeadine from the total alkaloids of petals of Papaver rhoeas L.A. preparative high-performance liquid chromatographic (HPLC) method with a LiChrosorb Si 60 column, using chloroform containing 0-5% (v/v) of methanol (isocratic and then linear gradient) as mobile phase, is described that allows the isolation of rhoeagenine from a few fractions issuing from the previous low-pressure liquid chromatographic run. Finally, a selective analytical HPLC method with a Superspher Si 60 column using chloroform-methanol (90:10, v/v) containing 0.1% of trifluoroacetic acid as mobile phase and UV detection at 292.5 nm is described that allows the determination of isorhoeadine and rhoeagenine in red poppy extracts. In comparison with a classical chloroformic alkaloid extraction of petals from Maine et Loire (France) (total alkaloid efficiency = 0.203% dry material), a weak aqueous alcoholic acidic extract (30% ethanol) (0.216%) and an aqeous acidic extract (0.123%) of the same material, the amount of isorhoeadine is 71.1, 42.4 nad 10.5 mg/g total alkaloids, respectively, and the amount of rhoeagenine is 629.7, 424.2 and 117.3 mg/g total alkaloids, respectively. Hence, the aqueous alcoholic acidic extract seems to be the most appropriate for conceiving a red poppy remedy. © 1992.