Eggs of several parasitic nematodes, particularly those of the gastro-intestinal tract of herbivores, cannot be identified to genus. Culturing nematode eggs in faeces results in the production of infective larvae. These larvae can then be identified, at least to genus.

Given suitable culture conditions, eggs of some nematodes will larvate, and then the larvae will hatch from the eggs and develop to the infective stage. This is usually accomplished by mixing freshly collected faeces with a substrate such as peat moss placing the mixture in a culture jar. The jar is kept moist, but not wet, and in the dark, for approximately two weeks. The larvae that develop can then be recovered from the culture using the Baermann technique. Different substrates, culture vessels and culture periods may be used. All may affect culture results. It is possible to quantify fecal cultures.

Fecal cultures are notoriously sensitive to culture conditions. Many aspects of these conditions may affect culture success. It is sometimes difficult to know whether the larvae that are recovered accurately reflect the eggs that were present in the initial fecal material, in other words, did eggs of all the species present in the faeces result in infective larvae recovered from the culture. Unfortunately, there is usually no means of checking this. In addition, if the fecal material is not freshly collected, it may be contaminated with larvae of free-living nematodes from the environment, which complicates larval identification.