A proline-rich polypeptide (PRP) complex, subsequently called Colostrinin, was isolated from ovine colostrum. The complex showed immunomodulatory properties in mice, rats, and chickens, inducing maturation and differentiation of thymocytes. It was recently found that Colostrinin is a cytokine-like factor that acts as an inducer of interferon gamma (IFN-gamma) and other cytokines in human peripheral blood and cord blood leukocyte cultures and has psycho-immuno-enhancing activity in volunteers. These observations prompted us to study the effect of Colostrinin on patients with Alzheimer's disease (AD). Forty six AD patients were divided into 3 groups and randomly assigned to receive orally either Colostrinin (100 microg per tablet, every second day), commercially available bioorganic selenium (100 microg selenium per tablet, every second day) or placebo tablets. One cycle of the treatment lasted 3 weeks and was separated from the next cycle by a 2 week hiatus. Each patient received 10 cycles of treatment during the year of the clinical trial. Outcomes were assessed by psychiatrists blinded to the treatment assignment. Eight of the 15 AD patients treated with Colostrinin improved and in the 7 others the disease had stabilized. In contrast, none of the 31 patients from the selenium or placebo groups with similar mild or moderate AD improved. The administration of selenium promoted stabilization in 13 of the 15 patients, whereas in the placebo group only 8 of the 16 patients were stabilized at the 12 month trials end-evaluation. Colostrinin was found to be a remarkably safe drug. Mild and transient effects were anxiety, stimulation, insomnia, and tiredness. The results obtained showed that oral administration of Colostrinin improves the outcome of AD patients with mild to moderate dementia. The results are very encouraging and deserve further research.