Transbronchial diagnosis of unexposed lung tumours is challenging in clinical practice. Although modified transbronchial needle aspiration (TBNA) is used for this purpose, the diagnostic yield is unsatisfactory. In such cases, conventional endobronchial ultrasonography with a guide sheath and transbronchial biopsy (TBB) is also ineffective. We found TBB was feasible by placing a guide sheath with a thin transbronchial needle into the tumours. We report two cases of unexposed tumours diagnosed successfully with this technique. Case 1 presents a typical carcinoid in the peripheral lung. Case 2 presents a squamous cell carcinoma at the third bifurcation of the right lung. TBB samples obtained this way were larger than TBNA samples. Moreover, multiple TBBs were possible once the guide sheath was inserted intratumourally. In the modern era of precision medicine, larger amounts of tissues are required for multiple downstream analyses. This novel technique will make a significant contribution towards diagnosing unexposed lung tumours.