In recent years, interest in determining the influence of moisture changes on the resilient modulus (M sub R) of subgrade soils beneath a pavement has increased. This is because the 1993 AASHTO "Guide for Design of Pavement Structures" recommends using a single M sub R value. The design M sub R is expected to account for the seasonal variation in subgrade moisture content. This study was undertaken to evaluate the variation of M sub R with postcompaction moisture content and suction of selected subgrade soils in Oklahoma. A sandy soil (S-Soil) and a clayey soil (C-Soil) were used for laboratory testing. The C-Soil specimens to be subjected to wetting were prepared by a modified compaction method. The proposed method was expected to enhance the flow of water in a specimen during the wetting process. New laboratory procedures for wetting and drying of specimens were also introduced and were used to establish correlations among M sub R, moisture variation, and suction. Results indicate that M sub R-moisture content relationships for C-Soil exhibit a hysteretic behavior due to wetting and drying. A similar behavior was observed for S-Soil. The C-Soil was more susceptible than the S-Soil to moisture variation, as expected. It was also observed that changes in M sub R values and suction were influenced by the initial (compaction) moisture content.