Abstract Circadian rhythms of serum testosterone concentrations in men have been shown, in general, to be highest in the morning and lowest in the evening. Thus, the purpose of this investigation was to determine the effects of acute resistance exercise upon the waking circadian rhythm of salivary testosterone over 2days (with or without resistance exercise). The subjects included ten resistance-trained men (with at least 1year of lifting experience) with the following characteristics [mean (SD)]: age 21.6 (1.1)years; height 177.8 (9.5)cm; body mass 80.5 (11.5)kg; percent body fat 7.9 (1.7)%. A matched, randomized, crossover study design was used such that each subject was tested under both the resistance exercise and control (no exercise) conditions. The resistance exercise protocol consisted of ten exercises performed for three sets of ten repetitions maximum with 2min of rest between sets. Saliva sample 1 was collected at 0615hours and resistance exercise began immediately afterwards at approximately 0620hours, and sample 2 was collected at 0700hours, which corresponded approximately to a mid-exercise (or control) time point. Saliva samples were then obtained every hour on the hour from 0800hours until 2200hours. No significant differences were observed between the exercise and resting conditions for salivary testosterone, with the exception of a significant decrease at 0700hours during the resistance exercise protocol. The results of this investigation indicate that resistance exercise does not affect the circadian pattern of salivary testosterone secretion over a 16-h waking period in resistance-trained men.