Introduction: Oral potentially malignant disorders (OPMD) are lesions associated with an increased risk of transformation (MT) into cancer. Objective: A study was made of the salivary levels of adenosine deaminase (ADA), ferritin (FRR) and total proteins (TP) in healthy individuals and in patients with oral potentially malignant disorders (OPMD), assessing the potential role of saliva as a diagnostic tool. Methods: A total of 91 subjects participated in the study, divided into two groups—59 patients with OPMD (oral leukoplakia or oral lichen planus) and 32 healthy controls—with measurements being made of salivary ADA, ferritin (FRR) and total proteins (TP). Results: There were no significant differences in salivary mean ADA between the OPMD group 0.85 ± 2.18 UI/I and the controls 0.71 ± 1.72 UI/I (p = 0.934), though the levels of both FRR mean OPMD, 12.66 ± 10.50 (µg/L), versus control, 7.19 ± 4.44 (p = 0.001), and TP, 23.41 ± 17, versus control, 14.15 ± 15.19, were significantly higher in the OPMD group (p = 0.001). Patients with oral lichen planus showed significant differences in terms of FRR (p = 0.009) and TP (p = 0.003). The ferritin in LPO with a cut-off point of 8.5C showed a sensitivity and specificity of 54.3% and 82.3, respectively. The area under the curve (AUC) was 0.69 (95% confidence interval (95% CI): 0.58–0.82; p = 0.003). Conclusions: Ferritin and total proteins may constitute potential salivary biomarkers for oral lichen planus, though further studies are still needed in this field. In addition, saliva testing is a reliable and noninvasive diagnostic tool and appears to be a reliable strategy offering an interesting alternative for the screening of large populations.