Grasping of stroke patients is often affected by improper coactivation of muscles controlling the fingers. The restoration of hand function therefore represents an important goal in rehabilitation. Quantitative data on coordination between fingers can be helpful for the assessment of therapy effectiveness. We have designed a novel isometric finger device to assess three-dimensional forces applied by the thumb, index, and middle finger. The device was used in connection with a simple virtual reality task where the patient had to open a safe by sequentially rotating a knob using the isometric finger input. The presented virtual reality application was evaluated in a group of healthy subjects and a chronic stroke patient to obtain preliminary performance results. We analyzed the coordination of fingertip forces between the thumb and opposing fingers. Pearson correlation coefficient was determined to assess the coordination of force in each direction. In healthy subjects, the analysis of the fingertip forces showed precise coordination of force between the fingers to control a virtual object. The performance of the stroke patient was considerably lower due to reduced muscle control and presence of strong spasticity. The results showed use of excessive force in both hands and lower coordination of force between the fingers as compared to the healthy subjects. The proposed virtual reality system is considered as a complementary method to the existing methods used in physical and occupational therapy. Specific virtual reality tasks could be designed to train coordination of force between the affected fingers.