Considerable variation in pre-laying behaviour of domestic hens (Gallus gallus domesticus) is observed within individuals, between individuals and between different husbandry systems. The contributions of internal and external factors to this variation were considered. The main internal factors considered related to lag and position of eggs in sequences. The duration of the sitting phase and the total time spent in the nest box was related to lag. The duration of pre-laying behaviour was longer for the first egg of a sequence than for the other eggs. This was mainly due to a longer searching phase in which hens performed more nest examinations. The duration of the sitting phase was longer for the last egg of a sequence than for other eggs; this may have been related to a longer lag found for the last egg. A series of experiments was conducted to investigate the performance of pre-laying behaviour while altering the availability of food and motivation to feed. Hens always interrupted their pre-laying behaviour in order to feed when food was presented. Length of deprivation did not influence the duration of feeding or pre-laying behaviour, that is, even "satiated" hens stopped their pre-laying behaviour and fed. However, the delay in oviposition was found to be greater when food was presented in the later, rather than the earlier, stages of pre-laying behaviour. The duration of pre-laying behaviour and of the searching phase was longer if hens were food deprived than if food was available. External factors examined included the effects of conditions that facilitate searching and nesting behaviour on pre-laying behaviour. Hens provided with an unlittered nest box showed an extended pre-laying behaviour and searching phase, more searching behaviour and nest examinations and more nest entries of a shorter duration than when provided with a littered nest box. Providing an exploratory walkway to facilitate searching behaviour resulted in the searching phase starting earlier than expected, and in the occurrence of more searching behaviour and nest examinations during this time.