Ilmofosine (BM 41.440, 1-hexadecylthio-2-methoxymethyl-rac-glycero-3-phosphocholine) is a synthetic alkyl lysophospholipid analog with activity against a variety of tumor modelsin vitroandin vivo.The i.v. form is presently undergoing early clinical investigation in phase 1 trials. In order to help define types of tumors that might be clinically sensitive to this agent we have studied the anti-tumor effects of ilmofosine against a variety of freshly explanted human tumor specimens using anin vitrosoft agar cloning system. Final concentrations of 1.0–30 μg/ml were used in continuous incubations experiments. Of 348 specimens tested, 134 (39%) were evaluable for determination of tumor growth modulating activity. The most common tumor types recruited included non-small cell lung, breast, colorectal, ovarian, renal cell cancer and melanoma. A concentration-dependent increase in the frequency of inhibited tumor specimens was observed with 6/134 (4%) sensitive specimens at 1 μg/ml as compared with 113/133 (85%) sensitive specimens at 30 μg/ml (pin vitro.Clinical phase II trials with Ilmofosine including the tumor types within vitrosensitivity are warranted if adequate plasma concentrations of this agent can be reached in patients.