Contact with darcin in male urine stimulates learning and subsequent attraction to airborne urinary odours specific to that individual male. Females were pre-exposed to full contact with urine test stimuli (A, C) or to airborne odours only (B) before being tested with airborne odours from a male versus female urine stimulus that could not be contacted during the test. Displayed is the total time spent under airborne urine stimuli from males (blue bars: urine; hatched bars: urine plus recombinant major urinary protein MUP) and females (pink bars), together with the difference in time spent under male minus female stimulus (circles), plotted as means ± standard error of mean. Significant P values indicate greater attraction to the male airborne stimulus (matched pair t-tests on log transformed data (t), or Wilcoxon matched pair tests (z) when transformed data did not approximate normality). Male urine stimuli: Wild1, Wild2 = random selection of wild-derived males; B6 = C57BL/6 inbred strain; Bc = BALB/c inbred strain; Bc + rd = r-darcin added to male BALB/c urine (11 μg in 10 μL urine); Bc + r94 = recombinant 18694Da MUP added to BALB/c urine (11 μg in 10 μL urine); Bc + r45 = recombinant 18645Da MUP added to male BALB/c urine (11 μg in 10 μL urine). A standard BALB/c female stimulus was used in all tests.