A series of isochromeno[4,3-c]pyrazole-5(1H)-one derivatives 7b-h were prepared and tested at 10 μM for their ability to displace specific [(3)H]flunitrazepam from bovine brain membranes. The substitution pattern of the above derivatives was shown to influence the receptor affinity. The most active compound of the series was 7e, showing a 54% inhibition of [(3)H]flunitrazepam binding. Compounds 7a-d,i were compared with the known isomers chromeno[4,3-c]pyrazole-4(1H)-ones 14a-d,i, showing that the isochromene/chromene isomerism influences the activity.