Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) given as a 24-hour infusion, and carboplatin have activity in advanced non-small cell lung cancer (NSCLC) and ovarian cancer. Two dose-finding studies were initiated to identify the optimal doses for the paclitaxel/carboplatin combination when paclitaxel is given in a 3-hour infusion. The fact that the pharmacologic interaction between paclitaxel and cisplatin increases the toxicity of paclitaxel when cisplatin is given before it also prompted an investigation of the influence of drug sequence on toxicity and pharmacokinetics in the NSCLC trial. Thirty-three patients with advanced NSCLC and 11 with advanced ovarian cancer previously untreated by chemotherapy have been enrolled to date. In the NSCLC trial escalating doses of paclitaxel were given in combination with a fixed carboplatin dose of 300 mg/m2, while both drugs were escalated in the ovarian cancer study. In both studies paclitaxel was infused over 3 hours and carboplatin over 30 minutes, and cycles were repeated every 4 weeks. The most frequent side effect has been neutropenia, although this did not result in any infectious episodes. Alopecia and mild emesis also have been frequently encountered. Mild skin reactions have been reported in a few patients. Bone pain and myalgia occur more frequently at the highest paclitaxel doses. No difference in toxicity has been observed thus far between the two drug sequences in the NSCLC study. Both studies are still accruing patients as the maximum tolerated doses of paclitaxel in combination with carboplatin have not yet been reached (carboplatin 300 mg/m2 with paclitaxel 175 mg/m2 in the NSCLC study; carboplatin 400 mg/m2 with paclitaxel 150 mg/m2 in the ovarian cancer study). An investigation of maximum tolerated doses with granulocyte colony-stimulating factor support is planned thereafter.