To assess differences between Africans and expatriates, we reviewed records of 100 patients with loiasis presenting to The Hospital for Tropical Diseases, London. Fifty-one were black Africans, and 49 were white expatriates. A history of Calabar swellings was more common amongst expatriates (P = 0.0001, OR 8.1), whilst eyeworm was reported more frequently in Africans (P = 0.0038, OR 4.2). Higher eosinophil levels (P < 0.0001) and filarial antibody levels, whether measured by immunofluorescence (P = 0.047) or ELISA (P < 0.0001) were present in the expatriates. Africans were more likely to have microfilaraemia (P < 0.0025, OR 7.3), and among microfilaraemic patients, Africans had denser microfilaraemia (P = 0.012). The sensitivity of microfilaremia as a screening test for loiasis was 75% in Africans and 29% in expatriates. The sensitivities of filarial antibody tests in Africans and expatriates were 81% and 100% for IFAT, and 28% and 93% for ELISA. Following treatment, 63% of patients were considered cured, 25% were lost to follow-up and 12% had a documented relapse. The differences between the two groups of patients could be caused by differences in the chronicity of loiasis, but other explanations are also discussed.