The objective of this study was to determine which of the Random, Competition, and Time-sharing models provides the best description of courtship in the male threespine stickleback (Gasterosteus aculeatus). A critical re-evaluation of experiments in this field revealed both theoretical and methodological difficulties. An attempt was made to correct these problems and provide a more quantitative and statistically valid approach to the motivational study of behavioural switching. Eighteen subjects were tested over four stimulus conditions in a modified double-interruption experiment, where they alternated between courtship and nest-related behaviour. The animals were visually presented with one or three females, with or without eggs in the nest. Assessments of motivational 'dominance' were made on the basis of incomplete visits and variation of visit durations. Data on time budgets, and temporal variability and associations were also analyzed. The results provided little support for the Competition model. In 33 of the 36 sessions, the Random model was accepted as a logical default when the various methods of assessment failed to support, or contradicted the Time-sharing model. The remaining assessments of Time-sharing (both female- and nest-dominant) may be considered as artefacts of the assessment procedure. Four possible explanations of these results were discussed with respect to experimental design and motivational theory.