An ethological study of courtship and reproductive behavior of the anabantoid fish, Trichogaster leeri (Bleeker), was conducted on 6 breeding pairs in aquaria. Sexual behavior in this species is characterized by stereotyped behaviors and a distinct temporal pattern of activities that presumably aids in species isolation. Data were taken on form and structural features of bubble-nests, colors of male and female, and behaviors occurring during daily or twice-daily 15-minute observation periods over a period of approximately one year. Spawning sequences usually last 2 to 5 hours in this species and are characterized by several different bout types (interactions between male and female), which may be initiated by either male or female. The major phases observed were: (1) prespawning preparatory phase (2) courtship phase (3) clasp (4) swimming inhibition (5) postspawning aggression and (6) interval between bouts. The prespawning phase in males is generally characterized by establishment of a nest-territory, development of breeding color, and elongation of dorsal and anal fin soft-rays. This phase in females is usually marked by increased abdominal plumpness and changes in color and body-markings. Strictly speaking, only the latter parts of this phase occur during spawnings. Spawning bouts (stages 2, 3, and 4 of the ethogram) comprise approximately 7% of all bouts and many of these do not follow an "ideal" pattern. Spawning bouts usually last 50-55 seconds with courtship requiring 12-15 seconds, the clasp about 25 seconds, swimming inhibition 2-5 seconds, and postspawning aggression 3-6 seconds. Female courtship butting precedes almost all spawnings and appears to release leading-to-the-nest, lateral spread display, and curving in sexually responsive males. Spawning bouts generally contain fewer female courtship butts than most other sexual bouts and a conspicuous difference exists between female courtship butting means in spawning and pseudospawning bouts. Although reproductive behavior in T. leeri is stereotyped, variation in form, sequence, and duration of components is evident. Flexibility and adaptability are common so that variation within certain limits may be tolerated and/or compensated for. Hyperaggressiveness, physiological condition, low sexual motivation, mechanical problems, and previous experience appear to be important factors in determining the success of sexual bouts in T. leeri. Reproductive color changes, body-marking changes, and sexual dimorphism provide visual stimuli that may aid in the synchronization of reproductive behavior.