Swiss male mice were individually-housed or maintained in groups of 8 from weaning until 80 days of age. At this time, the grouped mice were allocated to new groups of 5-6 previously unfamiliar individuals. Identified dominants were then caged with two clearly submissive males for 1 week. At this time hypothalamic samples were taken from the dominant and one subordinate and from a number of long-term individually-housed males. A radio- immunoassay for LHRF was carried out. The levels of this hypothalamic releasing factor were significantly higher in both dominant and subordinate grouped mice than in 'isolates'. Mice of differing social status showed comparable titres of this hormone. The results suggest that social conflict and/or disturbance augments this factor in mice irrespective of the social status achieved by individual animals.