Four methods of observing and measuring root proliferation of sorghum plants were compared. Plants were grown under artificial lighting in portable lysimeters of 160-liter capacity. The two nondestructive methods were (1) measuring roots visible through glass in place throughout the 77 to 80-day growth period, and (2) measuring roots through ports covered with polyethylene film, which was pressed against the soil by 3.5 kPa2 of air pressure. This method is new. Destructive methods were (3) measuring length, and (4) weighing roots recovered from soil samples. The polyethylene-covered ports gave good visibility and adjusted to the moderate shrink-swell movements of the sandy loam soil. In contrast, gaps developed between glass and soil in the upper half of the 108-cm-deep lysimeters. Lack of contact between glass and soil and proliferation of roots intercepted by the glass hindered accurate observation. Root-growth rates, measured through polyethylene-covered ports, correlated significantly with those from soil-recovered roots, but growth rates measured through glass panels did not. Because far fewer roots were measured by nondestructive techniques, they had greater data variance than measurements of soil-recovered roots.