Males from different iguanian lizard species engage in frequent visual signaling during agonistic interactions, mainly by displaying head bobs. We conducted a detailed study of the structure of head bob displays mediating male agonistic interactions in Liolaemus lemniscatus lizards. We staged pair-wise encounters where one male, the intruder, was placed in the terrarium of a conspecific male, the resident. During these interactions, males exhibited only one type of head bob display made up of three distinct units: a low amplitude bob (unit 1), a brief pause (unit 2), and two consecutive high-amplitude bobs (unit 3). Head bob displays occurred singly or as a part of a bout, with a mean number of head bob displays per bout of two. Total head bob display duration was stereotyped. The highest inter-individual variation (duration and amplitude) was recorded for unit 3, suggesting that this unit may provide information about the individual identity of the sender. Winners of interactions performed more head bob displays than losers, and these were composed of units of longer duration and higher amplitude than head bob displays exhibited by losers. Although preliminary, our results suggest that, in L. lemniscatus, head bob displays may facilitate opponent assessment by conveying information about individual fighting ability, motivation, or dominance status.