The effect of the intensity of odour signals has rarely been investigated in the regulation of odour-guided behaviour in young mammals. This series of experiments used the mammary pheromone (MP) of the female rabbit to assess the influence of stimulus concentration on neonatal pup responsiveness. The MP is a single compound isolated from rabbit milk that releases in pups the typical head searching and oral seizing behaviour. The pups (n = 621) were exposed to graded concentrations of the MP in bioassays varying in stimulus delivery conditions. Experiment 1 demonstrated that in aqueous dilutions the MP efficiently elicits behavioural responses only within a limited range of concentrations (from 2.5 x 10(-9) to 2.5 x 10(-5) g/ml). Experiment 2 yielded the same outcome with highly purified MP delivered in dynamic conditions with a gas chromatograph. Finally, Experiment 3 used deodorized milk as the solvent of the MP; despite this change in the physico-chemical context of stimulation, similar results were reached.