Colic is a common gastrointestinal disorder of horses. The aim of this study was to find the correlation between the serum alkaline phosphatase activity and serum bile acids values and colic with regard to diagnosis, probability of surgery and prognosis, and to find the correlation between faecal pH and colic. Another aim of the study was to investigate the causative effect of specific biogenic amines (serotonin, tryptamine, tyramine, putrescine, cadaverine, histamine, spermidine, spermine, dopamine) in both faeces and blood and specific faecal bacteria (Clostridium perfringens, Clostridum difficile, Salmonella spp.). During the 8 months hospital-based study, 249 horses suffering from colic arrived at the hospital. Faecal and blood samples were taken from colic horses on the day of admission (FFS, n = 177 and FIBS, n = 187, respectively) and 3 days after admission (SFS, n = 70 and SIBS, n = 26, respectively). In addition, faecal samples were collected from non-colic horses (n = 34). In regard to investigated bacteria, C. perfringens was identified in 15.2% of FFS, 2.85% of SFS and 8.8% of the faecal samples from non-colic horses. C. difficile and Salmonella spp. were identified in none of the investigated faecal samples. Mean faecal pH of the SFS (7.02 +/- 0.71) was significantly lower than that of the FFS (7.12 +/- 0.56, p=0.02). Tryptamine in faeces was found in one colic sample (10.84 nmol/g) and 11 non-colic horses (5.43 to 10.99 nmol/g). Cadaverine and putrescine were identified in all faecal samples from both colic and non-colic horses. However, the studied amines were not identified in blood samples. In conclusion, this study provides evidence that the studied bacteria and biogenic amines could not be causative factors for colic in horses. Serum ALP activity and serum bile acids may not be of use for diagnosis, understanding probability of surgery or prognosis.