To determine whether the severity of illness of hospitalized patients participating in Phase 1 trials has changed, a modified APACHE II (MA II) index was used to evaluate retrospectively each Phase 1 patient admitted during September through December 1983 and the same 4-month span in 1987. During the 1983 period, 28 patients were enrolled in 13 Phase 1 protocols. Their average length of stay (LOS) was 12.6 days (±12.3 SD) with a mean MA II of 3.44 (±2.69 SD). During the same 4 months in 1987, there were 37 patients enrolled in 18 Phase 1 trials with a mean LOS of 13.5 days (±13.4 SD) and a mean MA II of 6.08 (±3.33). As indicated by MA II scores, 1987 hospitalized patients enrolled in Phase 1 trials had a higher severity of illness than did 1983 Phase 1 patients (p = 0.01). The implications of an oncology patient population with an increasing severity of illness are examined in relation to nursing staff forecasting, resource allocation, and productivity.