The relationship between blood cocaine concentrations and pharmacological effects is of both theoretical and practical interest. This study utilized a computer-assisted smoking device for the delivery of three active doses (10, 20, and 40 mg) of cocaine base to seven human volunteers. Doses were administered in an ascending dose design with random placement of placebo. Physiological, subjective, and performance measures were collected concurrently with blood samples. Mean peak plasma cocaine concentrations were achieved at 2 min after the 20-mg and 40-mg doses and at 5 min after the 10-mg dose. Maximal responses in systolic and diastolic blood pressure, "feel", "good" drug, and drug "liking" subjective effects were also achieved immediately after drug administration. Pupil diameter and heart rate increases demonstrated a modest counter-clockwise hysteresis in relation to plasma cocaine concentrations shortly after dosing. Systolic and diastolic blood pressure, heart rate, and some subjective and performance measures of drug effect demonstrated a biphasic response after smoked cocaine. Initial increases above baseline levels were followed by an apparent compensatory decrease below baseline levels at a later time after smoked cocaine. Despite evidence of hysteresis and biphasic responses for some measures, linear correlation was obtained between mean plasma cocaine concentrations and several pharmacological effects over a period of 4 h after dosing. Several subjective and cardiovascular measures returned to baseline levels in the presence of detectable concentrations of cocaine.