The June 6, 2000 coronal mass ejection was an exceptional full halo, which made it possible to measure cosmic ray (CR) decrease with a simple experimental set-up. Variation in the local secondary cosmic ray density has been investigated by means of gamma rays. The experiment site was located in Istanbul (41.1N, 29.0E). CR electrons and slow gamma rays have been eliminated. The CR density has dropped drastically starting on June 8, 2000. The counts have been compared with the pre-shock levels and some other cases of CMEs. During strong solar modulation, the local counts of secondary CR intensity values dropped down as much as 24%. (C) 2002 Elsevier Science Ltd. All rights reserved.