The effect of varying the frequency and duration of exposure to a mature boar on attainment of puberty in gilts was examined in two experiments. In Experiment 1, gilts received full boar contact for 30 min per day from 175 days of age on (a) 0 days per week (isolated), (b) 2 days per week (c) 5 days per week or (d) 7 days per week until puberty or 235 days of age. These treatments were replicated in January, May and October and a total of 97 gilts were used. In Experiment 2, conducted in September, gilts received full boar contact from 160 days of age for (a) 0 min per day (isolated), (b) 2 min per day, (c) 10 min per day or (d) 30 min per day each day until puberty or 240 days of age. In Experiment 1, neither frequency of contact nor month affected the proportion of gilts which reached puberty in response to boar exposure (0.92 overall). Among gilts isolated from boars, the proportion reaching puberty was significantly affected by month, being lower than that for boar-exposed gilts in January (0.0 vs 0.88, P < 0.01) and May (0.44 vs 0.92, P < 0.05) but not in October (0.71 vs 0.96, P > 0.05). The mean interval to puberty for isolated gilts in both May (48.0 days) and October (44.6 days) was longer ( P < 0.05) than that for any of the boar exposed groups, among which the interval was affected by month of exposure. In January the mean interval to puberty was similar at all levels of boar exposure (36.4, 34.3 and 28.7 days for 2, 5 and 7 days per week respectively) but was significantly shorter ( P < 0.05) for the 7 days per week gilts in May (32.6, 33.8 and 11.4 days) and for both the 5 and 7 days per week gilts in October (32.3, 18.4 and 16.5 days). In Experiment 2, the proportion of gilts which reached puberty in the 2 min (1.0), 10 min (0.71) and 30 min (0.92) per day groups did not differ significantly. Overall, more boar exposed than isolated gilts reached puberty (0.88 vs. 0.46, P < 0.05). The mean interval to puberty for isolated gilts (58.5 days) was longer ( P < 0.05) than for any of the boar exposed groups, among which the interval for the 10 min (7.4 days) and 30 min (11.7 days) per day groups was shorter ( P < 0.05) than for the 2 min per day group (24.9 days). All boar exposure treatments stimulated puberty in a high proportion of gilts but the response was either fast, resulting in a short interval to puberty or slow, resulting in a longer interval. We conclude there is a threshold level of stimulus required for a fast response and that this level changes throughout the year being highest in January (summer) and lowest in October (spring).