New, simple, low cost and sensitive ion-selective electrodes are described for the determination of some 1,4-benzodiazepines in their pharmaceutical preparations as well as in biological fluids. Drug-tetraphenylborate and drug-phosphotungstate ion pairs have been prepared and used as electroactive materials. Poly(vinyl chloride) (PVC), and poly(ester-urethane)s (UPCLs, UPBA, and UPDEGA) are used as the matrix. The proposed sensors give rapid Nernstian responses for 10(-4)-10(-6) M of the above mentioned drugs in a pH range of 3-7. The membranes developed have potential stability for up to 4 weeks and show high selectivity for the investigated drugs over many interfering ions. The electrodes are used for determining trace amounts of bromazepam, clonazepam and diazepam in their pharmaceutical preparations as well as in biological fluids. For pharmaceutical preparations, the relative standard deviation (RSD) values were in the range, 1.37-4.1, 0.7-2.52 and 0.3-1.2% for bromazepam, clonazepam and diazepam, respectively using the PVC based electrodes, while for the UPBA based electrodes, the (RSD) values were in the range 0.6-3.35, 0.7-2.45 and 0.6-2.41%. For biological samples, the RSD values were 0.64-1.88, 0.37-1.8 and 1.36-3.57% for bromazepam, clonazepam and diazepam, respectively. Comparison of the results obtained using the proposed electrodes with those found using a (HPLC) reference method showed that the ion-selective electrode technique is sensitive, reliable and can be used with very good accuracy and high % recovery without pretreatment procedures of the samples to minimize interfering matrix effects.