This study was designed to confirm or negate findings from earlier trials demonstrating that Colostrinin, a novel compound derived from ewes' colostrum, has potential in the treatment of mild or moderate Alzheimer's Disease (AD). 105 patients were recruited from six psychiatric centres in Poland. The trial consisted of a 15 week double-blind phase comparing Colostrinin with placebo, followed by a second 15 week open labelled phase when all patients received Colostrinin. The dosage of Colostrinin was 100 microg on alternate days for three weeks followed by two weeks drug-free. This cycle was repeated three times for each phase. The primary outcome measures used were Alzheimer's Disease Assessment Scale-cognitive portion (ADAS-cog) and Clinical Global Impression of Change (CGIC). Secondary outcome measures were Instrumental Activities of Daily Living (IADL); Mini-Mental State Examination (MMSE); ADAS-non cognitive test (ADAS-non cog); and overall Patient Response. The main outcome measures were assessed at week 15 when active was compared with placebo but all parameters were evaluated at baseline, week 15 and week 30. Two separate statistical analyses were undertaken, a Full Sample Analysis (FSA) in which all missing values were replaced with the worst result observed and a Valid for Efficacy (VFE) analysis in which those patients who had serious protocol violations were excluded. This resulted in 14 patients being excluded from the VFE-analysis. The FSA analysis at week 15 showed a stabilizing effect of Colostrinin on cognitive function in ADAS-cog (p = 0.02) and on daily function in IADL (p = 0.02). The overall patient response was also in favour of the active (p = 0.03). Patients graded as mild on entry also showed a superior response of ADAS-cog compared with more advanced cases (p = 0.01). Evidence from this study indicates an early beneficial effect on cognitive symptoms and daily function. Colostrinin has potential value in the treatment AD.