Toxoplasma is known to infect ~20% of the human population in the UK but is not considered a major cause of disease. However, there is an old saying "you will not find something unless you look for it". This presentation reflects my experience in a teaching hospital in Oxford, UK where pathologists knew of my interest in Toxoplasma (unrelated to my role in providing an ultrastructural diagnostic service). I had access to anti-Toxoplasma stage specific antibodies (tackyzoite-SAG1 and bradyzoite-Bag1). In the UK, where clinicians know of Toxoplasma in theory, it is rarely considered in differential diagnosis, except in cases of pregnancy. In other difficult cases, I was asked to examine pathology sections using immuno-cytochemistry to identify the presence or absence of Toxoplasma. In a period of 10 years, 10 cases were diagnosed at biopsy or autopsy plus two cases of congenital infection. These ranged from a middle-age woman (with unexplained headaches) to transplant patient (with negative serology). All the cases, except for the congenital cases, appeared to be associated with recrudescence rather than primary infection. In all cases, host tissue destruction is due to the uncontrolled proliferation of the tachyzoite stage. The devastating effect of uncontrolled proliferation will be illustrated. On review, most of these cases were subsequently shown to be associated with patients with a possibly impaired immune system. It is possible that earlier diagnosis and treatment could have prevented death but still cause some morbidity. In the congenital cases (diagnosed at 20 and 32 weeks scans due to foetal abnormalities), when the blood samples, taken at 12 weeks, was examined they were positive for Toxoplasma antibodies consistent with a recent primary infection. However, Toxoplasmosis is not routinely checked for in pregnant women in the UK. Could treatment at 12 weeks have protected the foetus? In adult cases, without the autopsy examination these deaths would have attributed to unknown infectious agent. Two changes could reduce the mortality: 1. Test the blood sample taken from pregnant women at 12 weeks for evidence of recent infection (IgM positive) and treat. 2. Check the immune status of patients with infections of unknown cause and, if immuno-compromised, consider Toxoplasma infection. From this local experience it could be suggested that Toxoplasma is an under diagnosed cause of mortality in the UK and probably many other countries.