The objective of this study is to assess the occurrence, distribution, and intensity of Gray Leaf Spot in Plateau State,Nigeria. Gray leaf spot (GLS) caused by Cercospora zeae maydis (Tehon and Daniels ,1925) has been recognized as one of  the most yield limiting diseases of maize worldwide. This disease, which causes severe lesions leading to defoliation and drying up of leaves. This also can lead to spread over a wide distance within a short time it is not promptly checked. Maize is a popular staple food crop in the north, west and mid-altitude of Nigeria. The consequences of GLS attacking maize in Nigeria can therefore adversely affect food sufficiency. Method and material that had been used are incubation on agar and pathogenicity test. Leaf and samples were collected from naturally infected maize plants from farms and research fields in Plateau State.  The samples were plated on blotter and nutrient yeast agar(NBY)  incubated at 28°C  for 4-8 days duration. Field inspection were carried out in both farmers and experimental  fields for the early and late planting seasons from 2000 to 2004 to monitor symptom evolution ,progression ,and also collect leaf samples of various stages to confirm the presence of the fungus. The Cersospora conidia were recultured on V8 medium and incubated at 28°C. As for pathogenicity test, Five hundreds seeds from each of the susceptible inbred lines were grown in the screenhouse for the test.Pure cultures of the two isolates A and B, obtained from the naturally infected plants and cultured on V8, and inoculated into plants.The first inoculation was carried out when the plants were six weeks old, followed by a second inoculation after two-weeks interval.The fungus was reisolated from the infected plants and plated in the V8 medium for confirmation. Result was obtained from the stages of symptom evolution observed in the field from 6-week-old plants until maturity. Based on macroscopic growth patterns and types on V8 medium (agar), there are four growth types, subculturing of each isolate on V8 medium produced abundant spores after four days of incubation, the pure cultures produced from isolated conidia exhibited the same difference in growth pattern, rate, and morphological characteristics and the production of toxin (cercosporin) and the cultures of the same isolated showed uniformity in growth and morphological characteristics. Pathogenicity test, there was no observation to observed on the 6-weeks old plants but symptoms were observed after a second inoculation when the plants were 8 weeks old. Pathogenicity tests with each of the isolated and combination of isolates exhibited the same symptoms as those observed in the field under natural infection. This study was able to provide information on the disease severity and symptoms with confirmation through a pathogenicity test. Two isolate exists in Nigeria, classified as A(cercosporin producing) and B(non cercosporin producing). The growth characteristics, conidia dimensions, and the production of cercosporin of the two isolates from naturally infected plants and from agar, showed that they were distinct. As conclusion, The presence of two isolates has been reported by Dunkle and Levy (2000) and Okari et al.(2003) and classified as groups 1 and 2.It has been reported that group 1 was prevalent in USA, while group 2 was found in both Africa and USA. These two pathogenic species with unknown abilities might combine and produce virulent pathotypes.