In medical humanitarian assistance, the diagnosis of diseases plays a crucial role. Laboratory investigations are one of the main diagnostic tools utilized in Médecins Sans Frontières' (MSF) programs. Currently MSF supports and/or operates more than 130 laboratories in approximately 45 countries. The variety of analysis offered depends largely on the context of the program and the availability of context adapted tools and ranges from sophisticated laboratories specializing in tuberculosis culture to small laboratories within a primary health care program or operating as mobile clinics. The largest laboratories in MSF are found in programs with the main objective to diagnose, treat and monitor patients with tuberculosis and/or human immunodeficiency virus. Other MSF programs are either disease-specific (e.g., malaria, Chagas, kala azar or visceral leishmaniasis, sleeping sickness, malnutrition, sexually transmitted infections) or are integrated in primary or secondary health care structures.