Necrotic enteritis (NE), a disease associated with high numbers of the intestinal bacterium Clostridium perfringens, is common in intensive broiler production. Antimicrobial feed additives may control the disease, but their use is now being questioned in many countries. A field study was undertaken at the end of 1997 to study the level of naturally occurring specific humoral immunity against phospholipase C (PLC; C perfringens alpha toxin) in Norwegian broiler flocks. Blood samples were collected at hatch from 61 study flocks, and the sampling was repeated for 56 of the same flocks at processing. The level of specific antibodies against PLC was analyzed in an enzyme-linked immunosorbent assay (ELISA) test. Data on production performance and weekly mortality were recorded. The relationship between the age of the hens and the level of specific maternal antibodies in the progenies was studied. The association between the level of the maternal antibodies and the production performance, including mortality, was analyzed. The level of specific antibodies against PLC in day-old broiler flocks was relatively high and varied considerably compared with the levels in the broilers at processing. The progenies from the oldest hens had significantly higher levels of specific antibodies than the chicks from younger hens. No outbreak of NE occurred during the study period, making it impossible to analyze the association between naturally occurring specific immunity against PLC and the occurrence of the disease. However, the results showed that the flocks with high titers of specific maternal antibodies against PLC had lower mortality during the production period than flocks with low titers.