The effects of zopiclone 7.5 mg in comparison to flunitrazepam 1 mg, triazolam 0.25 mg and lormetazepam 1 mg on stages of information processing in a memory-scanning task were investigated in 10 normal volunteers using a double-blind placebo-controlled cross-over design. Overall reaction times for the test were significantly increased 1 h following treatment with zopiclone, flunitrazepam and triazolam and in the morning following nighttime medication with flunitrazepam. The effects of zopiclone, flunitrazepam and triazolam were found to be located in the serial comparison and response-selection organization stages of the reaction process although both flunitrazepam and triazolam caused additional impairment of stimulus encoding.