We determined the activity of lysozyme recovered from various conventional and silicone hydrogel (SH) contact lens materials as a function of time, using an in vitro model. Polymacon, omafilcon, etafilcon, vifilcon, lotrafilcon A, lotrafilcon B, balafilcon A, galyfilcon A and senofilcon A contact lenses (n = 5) were incubated in lysozyme solution for time periods ranging from 1 h to 28 days. Following the specified incubation period, the lysozyme deposited on the lenses was extracted and the sample extracts were assessed for lysozyme activity and total lysozyme. We found no significant difference (NSD) between omafilcon and polymacon lens materials for the initial 3 days (P > 0.05); however, there was a significant difference between the two lenses from 5 to 28 days (P < 0.05). There was NSD (P > 0.05) between etafilcon and vifilcon lens materials at all time-points and significant differences were seen between various SH lens materials at different time points. After 28 days, lysozyme deposited on etafilcon (90 +/- 3%) and vifilcon (91.4 +/- 3%) exhibited the greatest activity. Lysozyme deposited on polymacon (17.8 +/- 4%), lotrafilcon A (23.4 +/- 4%) and lotrafilcon B (24 +/- 5%) exhibited the lowest activity. Lysozyme deposited on omafilcon, galyfilcon, senofilcon and balafilcon exhibited 38 +/- 3%, 62.3 +/- 8%, 47 +/- 6% and 61 +/- 7% of activity, respectively. The reduction in activity of lysozyme deposited on contact lens materials is time-dependent and the rate of reduction varies between lens materials. This variation in activity recovered from lenses could be due to the differences in surface/bulk material properties or the location of lysozyme on these lenses.