Antibody reactivity against survivin, a recently identified tumor- associated protein, was determined in sera from patients with lung (n = 51) or colorectal cancer (n = 49). The same collection of sera was tested for the presence of antibodies against p53. Eleven sera from lung cancer patients and four sera from colorectal cancer patients reacted with purified recombinant survivin in an ELISA (21.6% and 8.2%, respectively), whereas four sera from lung cancer patients and nine sera from colorectal cancer patients contained anti-p53 antibodies (7.8% and 18.4%, respectively). The increase in prevalence when anti-survivin and anti-p53 antibodies were determined in parallel was statistically significant (29.4% versus 7.8%, P = 0.005 in lung cancer population; 26.6% versus 8.2%, P = 0.015 in colorectal cancer population). The high prevalence of anti-survivin antibodies makes these antibodies an attractive novel marker for the diagnosis of lung and colorectal cancer, particularly in patients lacking anti-p53 antibodies.