A hybrid technique of the Laplace transform and finite-difference methods in conjunction with the least-squares method and experimental temperature data inside the test material is applied to investigate the spray cooling of a hot surface. In this study, the unknown surface temperature and heat flux will be predicted. Their functional forms are unknown a priori in the present study and are assumed to be the functions of time before performing the inverse calculation. The whole time domain is divided into several analysis sub-time intervals and then these unknown estimates on each analysis interval can be predicted. In order to validate the accuracy of the present inverse method, comparisons between the present estimates and previous estimated results are made. The results show that the present estimates of the unknown temperature at various measurement locations agree with the previous estimated results and experimental temperature data. However, the present estimates of the unknown surface heat flux deviate from the previous estimated results for larger times. (C) 2007 Elsevier Ltd. All rights reserved.