In this paper, an improved identification algorithm is presented for continuous-time delay systems under unknown initial conditions and disturbances for a wide range of input signals expressible as a sequence of step signals. It is based on a novel regression equation which is derived by taking into account the nature of the underlying test signal. The equation has more linearly independent functions and thus enables to identify a full process model with time delay as well as combined effects of unknown initial condition and disturbance without any iteration. Unlike the method in Wang et a]. [Q.-G. Wang, M. Liu, C.H. Chang, W. Tang, Robust process identification from relay tests in the presence of non-zero initial conditions and disturbance. Industrial and Engineering Chemistry Research 45(12) (2006) 4063-4070], this new algorithm requires no process data before the test starts. Its effectiveness is demonstrated through examples. (C)) 2006 Elsevier Ltd. All rights reserved.