With the development of new therapeutic strategies, and the concept of mild cognitive impairment (MCI) as an early stage of Alzheimer's disease (AD), there is an increasing need for an early and accurate diagnosis of sporadic AD. Therefore, biological markers allowing a positive diagnosis early in the course of the disease are highly desirable. The most extensively evaluated markers of sporadic AD are amyloid-beta proteins and levels of both total and phosphorylated microtubule-associated protein tau. In this study, we review the currently available data on the aforementioned markers assessed in the cerebrospinal fluid or plasma, alone and in combinations, focusing on their clinical applicability including sensitivity in the diagnosis of AD and mild cognitive impairment, specificity in discriminating AD from other dementias and correlations with the disease progression and apolipoprotein E genotype. We also analyze advantages and potential drawbacks of using biomarkers in the laboratory diagnosis of AD.