________________________________________ * Author for correspondence; E-mail: brazen_sarkar@yahoo.com Int. J. Chem. Sci.: 10(1), 2012, 19-26 ISSN 0972-768X www.sadgurupublications.com CYTOTOXIC, ANTIBACTERIAL AND FREE RADICAL SCAVENGING ACTIVITY STUDIES OF THE SOLVENT EXTRACTS OF AERIAL STEMS OF EQUISETUM DEBILE ROXB BRAZENDRANATH SARKAR a,b* , S. M. ABU RAIHAN, NASIM SULTANA a , RAQUIBUR RAHMAN b , MOHAMMAD EMDADUL ISLAM, SHAMIM AHMED a and SHAKILA AKTER a National University, GAZIPUR, BANGLADESH a Bangladesh Council of Scientific and Industrial Research (BCSIR) Laboratories, Dr. Qudrat-i-Khuda Road, DHAKA, BANGLADESH b R & D Biotech., INCEPTA Pharmaceuticals Ltd., Zirabo, Savar, DHAKA, BANGLADESH ABSTRACT The cytotoxic potential of the different solvent extracts of Equisetum debile were examined by using brine shrimp lethality bioassay. However, n-hexane, ethyl acetate and n-butanol extract exhibited quite potent activity in brine shrimp lethality bioassay with LC 50 4.25, 3.36 and 4.40 µg/mL, respectively. These result suggested that they might be contain antitumar or pesticidal activity. Further, ethyl acetate extract showed significant free radical scavenging activity with IC 50 24.8 µg/mL. On the other hand, ethyl acetate and n-butanol extract demonstrated excellent antibacterial activity with a zone of inhibition of 9 ± 1mm against the tested pathogenic microorganisms. Key words: Bioassay, Cytotoxicity, Free radical scavengers, Antibacterial screening, Equisetum debile Roxb. INTRODUCTION General bioassays that exhibit capable of detecting board spectrum of bioactivity present in crude extracts are brine shrimp lethality bioassay (BSLT) and free radical scavenging activity test (FRST). Both techniques are easily mastered, low cost, and needs small amount of test material. BSLT is predictive cytotoxicity and pesticidal activity 1 . This test has been introduced in 1982 2 and employed for bioassay-guide fractionation of active