The objective of this study was to identify multiple plasma protein markers that might be characteristic of in situ and invasive cervical cancers. Plasma samples obtained from patients with in situ cervical cancer (carcinoma in situ [CIS], n = 32), from patients with early invasive cervical cancer without lymph node metastasis (squamous cell carcinoma [SCC], n = 60), and from age-matched disease-free controls (n = 37) were analyzed by cation-exchange protein chips and surface-enhanced laser desorption and ionization time-of-flight mass spectrometry. A classification tree defined by six protein peaks could discriminate 84 of the 92 cancers (CIS and SCC) and 36 of the 37 controls, with 91% sensitivity and 97% specificity. In comparing the CIS and SCC samples, two protein peaks with Mr values of 6586.41 and 3805.68 were able to classify 55 of the 60 SCC and 31 of the 32 CIS samples, with 92% sensitivity and 97% specificity. This study demonstrates for the first time the feasibility of differentiating in situ and invasive cervical cancers through plasma protein profiling. Identification of the proteins different in invasive and in situ cancer may be of great value in the understanding of cervical cancer invasion and in the development of novel therapeutic intervention.