Male (a, c) and female (b, d) wild type (Mdk +/+, filled circles) and homozygous midkine knockout (Mdk −/−, open squares) mice underwent a modified DID test, in which they were provided 20% ethanol in water (v/v) for 4 h per day, 4 days per week for 4 weeks. (a, b) Ethanol consumed in g ethanol/kg body weight/4 h during the first week of the DID test. There were significant effects of genotype for males and females and a significant effect of day for females. (c, d) Average ethanol consumed each week, expressed as g ethanol/kg body weight/4 h. There was a significant effect of genotype in males. Male Mdk +/+, n = 9; male Mdk −/−, n = 9; female Mdk +/+, n = 7; female Mdk −/−, n = 7. * P < 0.05 by two-way ANOVA. Data are presented as the mean ± SEM.