A method for reducing the number of transitions generated by an LFSR is introduced. The transition monitoring window monitors the number of transitions occurring as random patterns generated from an LFSR are applied to a scan chain, and, if the number of transitions exceeds a threshold value ("k-value"), all further transitions are suppressed. The transition monitoring window monitors the patterns entering the LFSR, incrementing a counter if a transition is detected. If a transition is detected just before the exit of a lowest stage of the LFSR the counter is decremented. The signal from the counter is compared with the k-value at every clock tick, and if the count is greater than the k-value, the vector most recently applied to the scan chain is re-applied to the scan chain; if it is less than the k-value, the output from the LFSR is applied to the scan chain.