Juvenile and adult male and female Swiss mice were fed one of four specially-formulated, pelleted diets containing respectively 8 percent saturated vegetable fat, 8 percent soya oil, 8 percent olive oil and 2 percent soya oil (with identities hidden from the experimenter) or a local commercial rodent food. It was intended to assess their impact on some blood indices linked to risk of coronary heart disease (CHD). Subjects were individually housed and their blood concentrations of cholesterol, high-density lipoprotein cholesterol (HDLC) and triglycerides were assessed. Clearly, these non-isocaloric diets differed in palatability, producing complex effects on growth as well as physiological measures. Many indices were influenced by age, sex, and the duration of dietary exposure. Interactions between factors were common but it appeared that males showed the greater increase in risk factors in response to some diets.