Scaling of CMOS technology is degrading the reliability of upcoming microelectronic devices. When the circuit design enters the nanoscale dimensions, the inputs have more influence on the circuit's reliability due to the circuit's internal noises and gate errors. In this paper, we will model the deterministic inputs probabilistically and analyze their effect on the reliability of digital circuits. The analysis is based on the Bayesian networks error modelling scheme. The simulations are based on MATLAB and show the important relationships among different deterministic inputs and their reliabilities. The results show the range of reliability values obtained by changing the deterministic input probability values. © 2011 IEEE.