In order to investigate the possibility of having pressure‐hole errors when measuring pressure during experiments on the flow of polymer solutions through dies, slit dies were constructed having various aspect ratios and various sizes of pressure hole. Each slit die has three pressure transducers mounted flush with the wall of one long side of the rectangular slot and, in the opposite side, three other transducers mounted through pressure holes. Measurements of wall pressure were taken on both walls along the longitudinal centerline of the die. In the present study, first Newtonian liquids of two different viscosities (INDOPOL polybutenes L‐50 and L‐100) were used. It has been found that the Newtonian liquids tested give rise to pressure‐hole errors, which are correlatable with the viscous effect alone. And then, three viscoelastic polymeric solutions were used. These were: 2% polyisobutylene (PIB) in decalin, 2% carboxymethyl cellulose (CMC) in water, and aqueous solutions of polyacrylamide (ET597) of varying concentrations: 0.6, 2.0, 4.0, 6.0, and 8.0 weight‐percent. The wall pressure measurements obtained in the present study show that substantial pressure‐hole errors are present when 0.6% ET597 solutions are being studied, increasing with volumetric flow rate and hole size, and that pressure‐hole errors are decreased as solution concentration is increased. It has been found that ET597 solutions of 6% concentration and higher give almost negligible pressure‐hole errors, i.e., they fall within the measurement error. This concentration dependence of pressure‐hole error indirectly corroborates the earlier findings by Han, who reported that polymer melts give no discernible pressure‐hole error. A general expression is proposed for correlating pressure‐hole error with hole size, viscous effect, and elastic effect. This correlation is then used to explain the observed difference in pressure‐hole errors for ET597 solutions of different concentration.