The crude venom of the scorpion Buthus martensi Karsch (MKV) was separated into seven fractions, MK1-MK7, by gel filtration on a Bio-gel P-30 column. Injection of MK2 i.p. and i.c.v. caused reduced activity and feeding in mice, whereas injection of MK3 and MK4 induced increased activity, salivation, convulsions, rapid and laboured breathing. MK2 inhibited adrenergic transmission in the rat isolated anococcygeus muscle (Acm), while MK3 and MK4 produced marked agonist-like (contractile) action on the Acm. MK2 was further fractionated on a Bio-gel P-10 column into nine fractions, of which three fractions, MK2d, MK2e and MK2f, were found to inhibit adrenergic transmission in the Acm. Fractionation of MK2 using ion-exchange and reversed-phase chromatography resulted in the loss of toxin activity. MK3 and MK4 were refractionated by perfusion chromatography on a BioCad workstation. Refractionation of MK3 using cation-exchange chromatography on a POROS HS column produced five fractions, of which three fractions, MK3a, MK3b and MK3c, produced agonist-like action on the Acm. Subfractionation of MK4 by cation-exchange chromatography on a POROS HS column resulted in six fractions, of which five fractions had agonist-like action on the Acm. From MK4b and MK4c, four fractions, MK4bl, MK4b2, MK4c2 and MK4c3, with agonist-like action on the Acm, were isolated by reversed-phase chromatography on a R 2/H 4.6 column. Thus, several active fractions exhibiting either inhibitory or agonistic activity were isolated from the MKV by a combination of gel filtration, ion-exchange and reversed-phase chromatographic methods.