Factors contributing to the variation in plasma lipoprotein (a) (Lp(a)) concentration were surveyed in an Aboriginal population (175 men and 219 women), aged 24-86 years, from Western Australia. The plasma Lp(a) levels were highly skewed towards low levels in this population, with a median of 84 mg/L and a mean of 166 mg/L. Approximately 20% had plasma Lp(a) above the threshold value of 300 mg/L, while 52% had Lp(a) levels below 100 mg/L. The most commonly occurring phenotype was apolipoprotien(a) S4. In this phenotype, Lp(a) concentrations ranged from not detectable to 468 mg/L. There was a positive relationship between cigarette smoking and plasma Lp(a) concentration in men. Apolipoprotein A1 and bilirubin were positively associated with Lp(a) in the 40-60 age group and a positive relationship between weight and Lp(a) concentrations was observed in those aged 60 years or over. Thus, although Lp(a) is mainly genetically determined, there are clearly other factors which contribute to variations in Lp(a) concentrations.