Male-male agonistic behaviour of Agkistrodon contortrix was studied in the laboratory. Contests occurred during the periods of mating (Feb.-Apr. and Aug.-Oct.). Thirteen staged dyadic trials were run and larger males (mass/length ratio) were scored as winners in 11 of the 13 trials. Evidence for dominant-subordinate relationships in this species was obtained. Nine agonistic acts were coded from direct observations and from films. Seven of the acts were used in sequential analyses of intra- and inter-individual transitions. Numerous transitions were significant in both intra- and inter-individual analyses. Sequences greater than two events were detected in 3 of 4 males in the intra-individual analysis. Males that won contests exhibited certain acts significantly more frequently than males that lost, but there was no significant difference in the mean durations of like acts. Larger (mass/length ratio) males were always successful in defending a mate during courtship and in deposing smaller males from potential mates. Males introduced to pairs in copula exhibited few courtship or agonistic acts toward the pair, and in no case did introduced males depose smaller males.