The purpose of this study was to evaluate the influence of a preceding intense cycling bout on subsequent running economy in female duathletes and triathletes. Thirteen female duathletes and triathletes (age = 27.5 ± 3.36 yrs.) took part in three testing sessions: (a) measurement of running economy at 169, 177, 196, and 215 m·min−1 and running VO2 max; (b) remeasurement of running economy and measurement of cycling VO2 max; and (c) a 45 minute cycling bout at 70% of cycling VO2 max, immediately followed by measurement of running economy. Intraclass correlation coefficients between Day 1 and Day 2 running economy values ranged from 0.31 to 0.78. A systematic difference occurred at 169 m·min−1 only, with mean VO2 being higher on Day 1 than Day 2 (p<0.02). Based upon dependent t-tests, significantly higher running economy values (p<0.02) but not blood lactate concentrations (p>0.02) following the submaximal cycling bout compared to the control condition (mean of Day 1 and Day 2), at each of the four test velocities were found. Therefore we conclude that running economy was significantly impaired following a 45 minute intense cycling bout in female duathletes and triathletes, but lactate values remained constant.