A total of 10 female and 10 male healthy subjects will be enrolled and will attend two treatment periods, separated by a 7-9 day washout. Over these two periods, two formulations of ACT-129968 (Treatment A: two capsules, 250 mg each; Treatment B: one tablet, 500 mg) will be administered in the sequence A/B or B/A to 10 subjects (5 females and 5 males) per sequence as determined by randomization.